Is the just released iOS 4.1 beta reporting fewer bars in more places, just like Apple said their next iOS update would? That's what we're hearing... but not (just?) on iPhone 4 -- iPhone 3GS as well.
iPhone 4 has better reception in better signal areas, worse reception in worse signal areas when "death gripped", and we're hearing that's holding true under iOS 4.1, but again the signal is being reported "better". You see fewer bars in low signal areas, so you have a better idea what will happen if touching it in the lower left hand corner -- it might drop off completely.
Here's a vastly over simplified analogy: imagine iOS 4 was a school that gave anyone (any iPhone) who scored over 20% an A (5 bars). iOS 4.1 would be a much stricter school where you had to get an 80% for that A (5 bars.