Yesterday's announcement of the iPhone 4S disappointed a lot of people, not just because of Tim Cook's low-key presentation. Many observers were expecting an all-new iPhone 5 with a larger display and a case design similar to the iPad 2. Instead, they got an iPhone 4 with a faster processor and better camera. As a practical matter, the functional difference between what was generally expected in the "iPhone 5" and what Apple actually delivered in the iPhone 4S isn't great. Apple is also going to sell a ton of iPhone 4S phones, regardless of what the pundits think.
The question is whether the iPhone 4S is an interim product designed to buy time in order to get a true 4G LTE model ready, or whether it represents an overall slowdown in product revisions by Apple. On the desktop, the iMac design hasn't changed much in years; the big changes have been internal, with minor cosmetic external revisions. The Mac Pro's external design has barely changed since it was introduced in 2006. There's an excellent chance that the next iPad will combine the iPad 2's physical design with a faster processor, higher-resolution display, and perhaps, a better camera.
Does it mean that Apple will slow down its product development cycles? Will Apple start releasing entirely new iPhones and iPads every 24 to 36 months? Longer product lives would certainly give Apple an opportunity to amortize tooling costs over far more units. It would also give Apple more time to develop completely new designs. After all, Apple will still be selling the iPhone 3GS when it ships the 4S, more than two years after it was first introduced. The 3GS is still a viable entry-level smartphone.
So, don't be surprised if the next iPad looks very much like the iPad 2, and if future iPad and iPhone exterior designs are changed less often. Apple may see no reason to issue an entirely new model every year, until competitors catch up.