To save power, the phone shouldn't be constantly trying to acquire a signal when it can't find one. It should try for 10-20 seconds, give up, then go to sleep, only waking every 30 seconds or so to try again, briefly.
Don't you guys remember Antennagate, where the following iOS update smoothed how fast the bars change? I bet if you did the same thing with a phone running iOS 2.0 it'd move instantly.