I remember reading something about the QID and why it wasn't terribly popular for a long time. The conventional wisdom suggested that an early ...e6 and ...b6 allowed White to take over the long diagonal, and often get tactical shots such as Nf3-xe5, Nc6xe5 Bg2xRa8, winning.
That similarity, however superficial, to playing ...e6 and ..b6 in the KIA has kept me from even being slightly interested in those positions for Black. And since I don't like the KIA as White...
I have another reason for not liking ...b6. I often try the old way of playing, with e6, d5 c5 pawn structure, and eventually a b7-b5 q-side attack is nice. If I have to play b5 in two moves, I won't be as happy. It's hard enough to get that sort of attack rolling in the first place!
In other words, It's just a matter of taste, and I think it's icky to play ...b6. I know, such hard core analysis for free! You can thank me later.
(BTW Castlerock, I haven't forgotten that I actually owe you some analysis, but I need the games first!)