Even now, the die is being cast. By 5pm today Pacific Time (1am tomorrow GMT), academicians will have lodged the last of their Oscar votes. On Sunday, these may or may not provide The King's Speech with the coronation so many expect. Yet even if, in spite of that avalanche of nominations, this doesn't happen, perhaps it won't matter all that much. This film can manage without Hollywood's ultimate accolade. It's built its own legend already.

It's not just the ecstatic reviews, the sackload of awards and the startling box office takings. This is a film that's had people queuing around the block to see it and standing up to applaud as the credits roll. Yet it's a low-budget costume piece of the kind the Brits have delivered so often before to no particular effect. Its triumph has therefore shattered much conventional wisdom.

We were told that these days, there's no longer a big-screen audience for small-scale drama. That older cinemagoers have become extinct. That Britflicks shouldn't expect to hit the jackpot: our home market's not large enough; deep-pocketed investors are needed but can't be found; there isn't enough public funding, and those who disburse what there is don't know how to pick winners; while even if the right films were to get made, they couldn't get into our own cinemas, let alone the rest of the world's.

We've now learned different, but to benefit from this lesson, there's something we need to know. Just why has The King's Speech been such a success?

Industry experts don't have the answer. If they did, they'd have anticipated what's happened, which they didn't. Now, they highlight prescience on the part of funders like Prescience and the UK Film Council, four-quadrant targeting, awards corridor positioning, brilliant marketing by Momentum, the British distributors, and smart string-pulling by their counterparts in America, the Weinstein brothers. Yet even they acknowledge that there must be more to it than that.

So, like many of the critics (and the Academy of Motion Picture Arts and Sciences nominators), they point to what they deem to be magnificent acting, a fine script, classy production design and, for that matter, impressive cinematography, costumes, editing, score and sound-mix. Yet, even if you're sure that all this esteem isn't at least a little excessive, since when was mere excellence enough to bring in the crowds? We're not talking about a classic (yet); we're discussing a hit. And those tend to strike a chord, not just parade merit.

The film's director, Tom Hooper, has opined that The King's Speech appears to be mining the same cross-cultural myths as the likes of Avatar. OK, so what myths are we talking about?

An American analyst has identified 10 key elements that locate the film firmly in the paradigm of The Karate Kid, thus revealing it to be a B-movie story decked out "in A-list rags", like other such exercises he disdains. For novelist Michèle Roberts, it's all about gender: "The damaged king, who by artistic sleight of hand is Everyman, can be restored to full potency when he gets his voice back. Then he can lead his people into war."

Persuaded yet? That's the trouble with this game. Anyone can play. If you want to fuel your theory with your own prejudices, who's to prove you wrong? There's not even much point in asking cinemagoers, since many theories will assume subconscious responses which their owners might not own up to even if they were aware of them. Still, some frequently offered interpretations seem perfectly commonsensical.

Perhaps it's a straightforward matter of triumph over adversity, with the tale adhering strictly to the rule so memorably spelt out in Tropic Thunder: "Never go full retard." Or it's a standard bromance, with a bit of class war table-turning and behind-every-successful-man-there's-a-strong-woman. All of these may be popular themes, but this film seems to deploy them less emphatically than plenty of others have done.

Consideration must therefore turn to the more glamorous, zeitgeisty notions that have been tossed into the frame. Nostalgia generated by hard times "accounts for the excess of admiration heaped on the deeply retro The King's Speech", in the eyes of at least one of the lefties that the film has annoyed. Some such thinkers blame the "Downton Abbey syndrome", that is, the perverse attraction of the trappings of poshness for the downtrodden victims of capitalist excess. That these should actually be the accoutrements of royalty itself (we're watching "a sort of cinematic royal wedding") provokes even deeper alarm. Yet the film dwells on grandiose spectacle far less than it might have done, or perhaps than its limited budget would have allowed.

The revival of national pride as a reaction to the supposed dissolution of social identity is another explanation that also distresses some. Still, it much cheers others. Here's Melvyn Bragg: "It seemed to me in the final minutes of that film, when like many around me I was deeply moved, that we either mourn the loss of what we had or wish to retain a version of it. Not unusually we want to be unique and to be seen to be unique."

It should perhaps be noted that wartime audiences applauded the real George VI's newsreel appearances just as our own applaud The King's Speech. Still, this film hasn't clicked only with the British. It's taken three times as much money overseas as it has here. Most of that's come from America, and niche theories as to why this should be so abound. The film's been considered "an allegory for the age of Barack Obama, another leader who has been celebrated, venerated, lionised for his ability, in challenging times, to move people with his words".

Alternatively, Americans have been said to rejoice at seeing a mere colonial socking it to the snotty Brits, who still dare to look down on their former imperial subjects. More fundamentally, the film's been seen as celebrating the new world's informal, touchy-feely values and faith in therapy at the expense of the stiff-upper-lip culture of the stuffy Europeans. "This is not about fixing a voice, but fixing a mind," notes one savant. "Friendship is a voyage into the unknown for Bertie. [Lionel] Logue is gluing him together." Some of the younger Brits who've been unexpectedly keen on the film may also have liked this angle. They may see it as a rejection of the oppressive attitudes of the older generation.

Time, perhaps, to take a breath. Maybe by now you're thinking one of two things. The King's Speech clearly presses an impressive number of highly effective buttons. Surely it must be the cumulative effect of all these separate impacts that induces audiences to succumb. Or, you may be concluding that the film has so many attractive aspects that almost everybody will be beguiled by at least one of them; the throng of enthusiasts is therefore made up of entirely disparate sub-groups.

It's easy to adopt either of these analyses, but perhaps each is a bit of a cop-out. When you look back at cinema's great successes, from Gone with the Wind to ET, or The Sound of Music to Jaws, it's hard to believe that any of them can be put down to a mere ragbag of ingredients. On the whole, the big-screen hit turns out to be not a fox that knows many things, but a hedgehog that knows one big one. So, since everyone else seems to have had a go, here's my stab at the riddle inside the enigma.

This is indeed a robust and well-executed human story, but it's not an exceptional one. For my money, it's the political dimension that's taken it into the stratosphere.

The film is about a leader, and it comes at a time when many of us feel that our leaders have let us down. We've learned that we can't expect them to solve our problems, but we'd at least like them to do their best. Yet from Westminster to the Arab world, they've been demonstrating that instead, they're in it for themselves. Bertie, on the other hand, wants only to do his duty. To achieve this, he's prepared to submit himself to both exertion and indignity. In return, he won't even get to exercise power, since he's destined to reign, not rule.

Boris Johnson sees the success of The King's Speech as demonstrating popular support for the hereditary principle. In one sense, he could be right. We've come to realise that democracy requires potential leaders to make us false promises; naturally they then fail to fulfil them. Bertie has no need to make promises, and thus no need to forgo his integrity.

He differs from most of the leaders we know of (archetypally Hitler, his antagonist) in that he doesn't want the job. People, like films, prefer reluctance in a hero with good reason. It's often been said that to want the top job should be enough to disqualify someone from actually getting it. Not for nothing is the speaker of the House of Commons ritually dragged unwillingly to his chair.

Bertie's vulnerability shows him to be one of us without negating the pomp that lends him glamour, as might an appearance on I'm a Celebrity. Though he's blue-blooded, he's not one of our own Bullingdon toffs, already blessed with every advantage that life can bestow. And unlike them, he won't be walking away if the game ceases to appeal to him. His brother, of course, does just that, his behaviour foreshadowing our own unfortunate obsession with personal rights and cravings.

In short, The King's Speech stands in for the real-life speech that we're all desperate to applaud. But what do I know?