I think that this is a faulty assumption. If there's one mistake that most people make on these forums, it's judging not-yet-released Apple products by last years parts and tech. Apple almost always comes out with new proprietary parts and configurations inside their devices to make them faster and smaller.
The best/most recent example of this is the battery from the iPad 2 and the new iPad. Almost identical form factor and battery life, yet the iPad 2 has a 25 watt-hour battery while the new iPad has a 42.5 watt-hour battery.
I can definitely see the same thing being done with the new iPhone; we'll see!
The new ipad is noticably thicker and quite a bit heavier than the ipad2 to accomodate the larger battery