Original iPhone released: June 29, 2007
Original iPod touch: September 13, 2007
iPhone OS 2.0 announced and demoed: March 6, 2008
iPhone 3G and OS 2.0 release date announced: June 6, 2008
iPod touch update: September 9, 2008
iPhone OS 3.0 announced and demoed: March 17, 2009
iPhone 3GS and OS 3.0 release date announced: June 9, 2009
iPod touch update: September 9, 2009
See the pattern? Here's what we can predict from it:
iPhone OS 4.0 announced and demoed: April 8, 2010
iPhone update, OS 4.0 release date announced: June 2010
iPod touch update: September 2010
Apple's Mac updates were once artificially tied to events like Macworld or WWDC so they had a media platform to use for their major announcements. This was part of Apple's stated reason for backing out of trade shows -- so they could release Mac updates on their own schedule, not the media's. That said, Macs are still largely dependent on other manufacturers' hardware cycles (mainly Intel's) for updates. This means that Mac updates are probably always going to be relatively sporadic and unpredictable.
iPhone and iPod updates, on the other hand, are far easier to predict -- so far, they've been coming out with almost clockwork precision. Particularly since Apple is now developing their own mobile CPUs, the company is beholden to no one else's release schedule. With the pattern that's emerged over the past three years, it's pretty clear that Apple is committed to a cyclical, 12-month schedule for its portable lines: OS betas in spring, iPhone and OS updates in early summer, iPod updates in late summer. it's not clear yet how the iPad will fit into all this, and it won't be until the device goes through at least one revision. In the meantime, we can all stop being surprised when Apple doesn't make iPhone or iPod touch hardware announcements outside of the cycle outlined above.
Thanks to TUAW reader Nick.