I've always suspected that the patent lawsuit was the main reason why the rumble feature was removed.
I personally will miss the rumble feature. Some games used it very well (could anybody imagine playing Rez (PS2) for example without it?), while in others it was just a gimmick. But I've used a rumble pad in all my controllers since the N64 era, and it's something I've come to expect out of my console gaming experience.
Doesn't matter anyway to me - not like I'm getting a PS3 at launch.