I'll probably get downvoted for this comment but in this case, I think Apple tried to hard-code in a reality distortion field with the bars and it backfired..

A heavily-biased 3G signal meter that shows 5 bars for over half the signal range seems to have been implemented in iPhone OS 2.1 back in 2008. Problems show up with that display implementation due to antenna being on the outside on iPhone 4 and crossing the threshold from 5 bars to "other".

AT&T on the other hand is recommending a more accurate approach instead of interpretting 50% as 5 bars.

Not sure why people are reading this as an AT&T issue.