Last month, perfectly timed for the start of the Christmas shopping season, Leicester Square hosted a red carpet premiere. In keeping with the theme of the launch, actors dressed as soldiers mingled with the celebrity-studded crowd.

Business as usual – except that this glittering event didn't celebrate the launch of a Hollywood movie but a videogame, Call of Duty: Modern Warfare 2. The show of confidence marked the moment that gaming claimed its crown as the largest entertainment industry in the world.

For the first time last year, sales of videogame software topped $40bn; making the global cinema box office takings of around $28bn look rather puny. And it's not just about size, it's trajectory. Game sales have grown at a rate of at least 10% a year over the last two decades, while the movie market is stagnant by comparison (it grew by only 1.8% in 2006-07) – and the music industry is contracting.

There is real excitement over the release of new games. Andrea Phillips, who designed the promotional game for the film 2012, and writes the Deus Ex Machinatio games blog says, "People are waiting in line outside their local games store to pick up the new hot game when it goes on sale at midnight." The 2008 midnight launch of a World of Warcraft expansion pack at HMV Oxford Street was the biggest the store had ever seen – 2,500 people.

But this ascent to global dominance has happened quietly. Radio 4 doesn't have a regular games-discussion slot. Game-creators don't sit on Jonathan Ross's sofa to chat about their latest project. When I asked Kirsty Lang, presenter of Radio 4's arts and culture programme Front Row, why computer games don't feature more at the forefront of media coverage of culture, she was candid: "I think it's because the people who are making and commissioning these programmes are still too old. Those of us in our 40s and 50s, who are making the decisions about what will feature in the programmes, don't really play computer games. When we've had ideas put forward about gaming, they've tended to come from the younger members of the team."

Adrian Hon, co-founder of London-based games company Six to Start, agrees games are still seen as being "for young people" even though many now carry 18 certificates. "People seem reluctant to talk about the fact that they're gamers," he commented. "It's perfectly fine for an MP to say that they're into noir movies, or crime fiction, or Coldplay – but if they said, "Yeah, I'm a big Modern Warfare fan," they'd come off looking bad."

Yet this is changing. James Wallis, lecturer in game design at the University of Westminster, says that the traditional "twitch" game, with its need for fast reflexes and its casual violence, is no longer the key growth market for computer games. "Lots of people out there have never played a computer game. Well, you will! All the advertising for Nintendo's DS and Wii consoles has been aimed at non-game-playing demographics. Young women. The over-60s. Families – not just the boys. Casual gaming is also a vast market: the Facebook game Farmville has 60 million players worldwide. That is more people than live in the UK. The people who sit down in front of a console to play Modern Warfare 2 are in the minority of gamers."

Female gamers are certainly on the rise. Research earlier this year by the NPD group found that the proportion of female console gamers went from 23% in 2008 to 28% in 2009, while figures from Nielsen suggested that women aged between 25 and 54 now make up the largest group of PC gamers. As a lifelong gamer myself (starting with Skool Daze on my 48K Spectrum, and currently obsessed with the atmospheric faux-Victorian online game Echo Bazaar), I'm certainly glad to feel that I'm no longer in such a small minority.

Tom Chatfield, arts and books editor of Prospect magazine, is hardly a sterotypical gamer. And in his forthcoming book about the games industry, Fun, Inc, he explains, "Games aren't standalone any more; they increasingly overlap with other things people like doing. Music, for instance – Guitar Hero and Rock Band are each worth well over $1bn. No big movie now is without its gaming counterpart. When talking about his new movie Avatar, James Cameron describes the filming process as being like in a videogame."

In fact he says, console games are now just a small fraction of the worldwide gaming industry. "Boxed and mainstream games come out of the US, mostly the west coast and Texas, from Japan and some – including the Grand Theft Auto series, which was originally created by a Scottish game developer – from the UK. But other markets are also crucial, including free, micro-payment-based online gaming that has hundreds of millions of people involved, especially across Asia. The biggest example is Maple Story, a role-playing game with more than 100 million subscribers – these games are free or very cheap to play, but allow players to pay very small amounts of cash for a huge spectrum of in-game items, abilities and advantages."

He suggests that it's the very playfulness of games that makes them seem juvenile: "We are programmed on a very deep level to want to play, but with our Protestant work ethic, play is viewed as pretty subversive. We still think that we have to put play behind us as part of what the adult and working worlds mean."

This is a fascinating thought. Non-gamers often think of gaming as a "pointless" pastime, but perhaps that pointlessness is really the point: instead of constantly having to be productive, why can't we spend time on activities purely because they're enjoyable? As games continue to grow in size and strength, as they are played in greater numbers by women, by older people and by people who can't afford expensive equipment, the playful way of approaching the world may also spread.

If Chatfield is right, it might be in breaking down the boundary between work and play, and in encouraging us all to play more, that games will end up making their greatest contribution to our culture.