On the "why would many people bother with 9 or 11 when so few even bother to go to 7" question - the audyssey people present the case on their web site that the extra channels in the front/wide are more important than the extra back channels. They say:

"Wide channels are much more critical in the presentation of a realistic soundstage than the Back Surround channels found in traditional 7.1 systems. Adding surround channels behind the listener has a very small impact compared to the increase in envelopment and soundstage width that the Wide channels provide."

I have a 6.1 setup, and I find their research/claims plausible. I want great, well-positioned dialogue, great in-movie music and background sounds, well-located just-of-the screen effects, etc. Philosophically, it has always seemed to me that going too crazy with back speakers doesn't seem like it will add much - there is only so much you can do with rain effects (and etc.). So I can see folks being interested in adding heights and wides even if they are not already up to 7.1 (e.g., me).

That said, putting those wides out at 60 degrees may be a limiting factor for many - it is kind of a weird angle/positioning.