We thought we’d had it all figured out.

When Apple bucked the trend of numerically naming the iPad by calling the Retina iPad the “new iPad” instead of the iPad 3, we thought it was a sure thing that they’d do the same thing for the next iPhone. The next iPhone, then, would be “the new iPhone” or the “2012 iPhone”, not the iPhone 5.

It made total sense, in a way: Apple doesn’t add a numeral to the end of its other products, like the MacBook Pro or the iPod Classic. They don’t even do it for the iPod touch, which is basically the most current iPod with all the phone guts stripped out. Why continue setting apart the iPhone as a sequel to the handsets that have come before when you can position it, not as an incremental update, but a timeless product in its own right: the Mercedes of smartphones?

That’s the way Apple handles the rest of its products, but with the invitation for today’s, and now Apple accidentally spilling the official name of the next iPhone on their website, it now seems clear that Apple is going to call the sixth-generation iPhone the ‘iPhone 5’ after all. Why would they do that?

We think there’s a couple of issues at play here.

The first one, we think, is simply an issue of expectation. Ever since the iPhone 4, consumers have been clammoring for the iPhone 5 by name. Remember when everyone was calling the handset that would become the iPhone 4S the ‘iPhone 5’ instead? Given the longer than usual delay between the iPhone 4 and the iPhone 4S, that’s almost a two and a half year length of time in which people primarily referred to the next major redesign of the iPhone as the ‘iPhone 5.’

The fact of the matter is that after about twenty-eight months of word-to-mouth about the upcoming iPhone 5, it’s just good marketing to capitalize upon the buzz. People have expected the ‘iPhone 5’ to be the next huge upgrade for so long, the name’s already got momentum and caché. It builds off of expectations: after so much anticipation for the ‘iPhone 5’, Apple is finally delivering.

After so much anticipation for the ‘iPhone 5’, Apple is finally delivering.

But we think that’s only part of it. Apple, after all, could probably call the next iPhone anything they wanted and sell enough of them to keep a medium-sized nation’s GDP afloat for a year. We think there’s another couple of reasons Apple is keeping a numeral in the iPhone’s name.

For one, Apple sells more than one generation of iPhone at a time, unlike almost any other product. Right now, for example, Apple is selling the iPhone 3Gs, the iPhone 4 and the iPhone 4S. That’s three iPhones Apple is selling at once, and when the iPhone 5 comes out, it’s possible the number of iPhones being sold in different markets for different prices will grow to four. Keeping the numeral in the name of the next iPhone, then, allows customers to easily distinguish which iPhone they want and which of the current iPhones available are “better” than the other iPhones.

(It’s true that Apple sells more than one 9.7-inch iPad right now — the iPad 2 and the new iPad — but we expect that this will change when they introduce the smaller 7-inch iPad mini next month: the iPad 2 continuing to be sold was just a stop-gap maneuver that allowed Apple to keep selling a cheaper iPad against inexpensive Android competitors while they finished up their sub-$300 tablet. When the iPad mini comes out, we expect the iPad 2 will likely go away, and the iPad line of tablets will bifurcate down separate branches: the 9.7-inch iPad and the iPad mini, both of which would be considered separate products, not different generations of the same product. But I digress…)

Maybe Apple’s signaling that they don’t expect the iPad to radically change every year from here on out.

Perhaps there’s another issue at play, though. Why would Apple take such pains to make the point that they are calling the third-generation iPad “the new iPad” and yet, six months later, call the sixth-generation iPhone the “iPhone 5?” Maybe Apple’s not contradicting itself, but is instead signaling that they don’t expect the iPad to radically change every year from here on out, just like its other products.

Look at the difference between the iPad 2 and the new iPad. Sure, the new iPad has a Retina Display and has a faster processor and a couple other spec bumps, but otherwise, it pretty much looks and feels like the iPad 2. Maybe Apple’s trying to de-emphasize the difference between iPads by just calling it “the new iPad” because they think that, like most of their other products, the iPad won’t change much every year: like Apple’s other products, the iPad will have a major redesign every once and a while, but otherwise it will continue to undergo a series of incremental performance updates every year, largely looking and feeling the same each generation.

If that’s true, Apple’s decision to call the next iPhone the “iPhone 5” seems to imply that they think the iPhone will continue to evolve rapidly every two years, not just seeing incremental improvements, but major changes in both functionality and design. Under this naming scheme, the iPhone 5 will be followed by an iPhone 5S that is mostly a performance update on the iPhone 5 before it. A year later, the iPhone 5S would be followed by the iPhone 6, which would boast not only a major design revision, but powerful new hardware and functionality (for example, NFC) that will fundamentally change the way you interact with your smartphone.

If you think about it, this makes a lot of sense. An iPhone is the most important and intimate computer most people carry around with them, and there’s just so much more we can do with them. Apple doesn’t want to market all iPhones the same way until they can stop revolutionizing the way we interact with our smartphones every two years, like clockwork. They want each and every iPhone to say right in its name that it is bigger and more important than the last.

Apple wants each and every iPhone to say right in its name that it is bigger and more important than the last.

The iPhone is a special product to Apple. It’s the product that has set up their fortunes and made the the biggest company in the world: the most iconic, best selling gadget the world has ever known just five years after its debut. If you were Apple, would you rock the boat and change the way you brand the latest and greatest iPhone when you didn’t have to?

Update: Here’s another awesome idea on why Apple’s not calling it anything but the iPhone 5: they have no intention of releasing an iPhone nano, iPhone mini or iPhone Pro. In other words, all other successful Apple products eventually become product families, but Apple intends to keep the iPhone singular. Makes sense, and would explain both why Apple decided to change the name sequencing of the iPad when they did — they intended to make it into a family of devices — and why Apple doesn’t add numbers to the name of the Apple TV: they expect to eventually turn that product into a family as well with the introduction of the Apple HDTV.