I simply don’t believe the speculation that the new iPhone rumoured to be released in (the American) Autumn 2012 will be ~10mm taller.

If this was the case, this could introduce fragmentation in the wonderful apps ecosystem that Apple has built to date. I cannot imagine Apple designers would even consider the possibility of allowing the “older” apps run in a letterbox mode with redundant black bars. Or, maybe, they plan to introduce dynamic scaling of apps in the next version of iOS; similar to the full-screen app scaling in Mac OSX Lion.