You have to assume we are going to see a 3g update to the pearl at some point, its the only form factor of the 4.5 devices that hasn't had a higher end update since it came out. However, since the original pearls don't seem to be getting in on any 5.0 action, there does seem to be a gap in their range to be filled.
It might just be that carriers haven't shown any interest in a new one, but one possible technical reason why we haven't seen a major upgrade to the range yet might be battery life.
I doubt rim would want to release either a bulkier device or one with noticeably worse battery life due to the additional features, especially since it is a form factor that is most likely to appeal to heavy phone users.
What kind of woman keeps their phone in their back pocket? I've never 'butt dialed' and the keys on the pearl are plenty big to to use, they're way bigger than the keys on the full-sized devices. Driving and texting without looking at the keyboard's very easy with a regular pearl.