If the accelerometer in the iPhone / Touch is anything like the accelerometer from my old PS3 controller - it's a bunch of super tiny metal bars and wires (and I "think" a magnetic base) - they look like they are designed to "flex" under forces in a certain axis. (causing a voltage to go across one of the little coils adjacent to the bar)
In short - no, it does not look like it would be affected by temperatures that humans can exist in. In EXTREME temps (greater than -20F) I'd sway that thought.
If that's true, you're right, normal temperature shouldn't affect it much. Hmm..?
As a report for my trial at the 20 degree (Fahrenheit) range this morning, mine worked fine. I was outside for about 20 minutes.