Like you, I'm all for keeping it simple. Please understand though that "simple" can mean different things to different people. For me, the simplest way to have imaging to at my sides is to place speakers there; the easiest way to have sound localized behind me is to have speakers there. Not a complicated concept to understand. I see people doing both, especially with the new hi-rez music formats. As larger amounts of storage becomes cheaper, there's no reason you can't have more channels and higher quality in each channel. More speakers wouldn't help high back theatre seating because they'd still block the sound from the rear speakers. High backs are just a bad idea for surround sound. Our ear/brain mechanism is able to localize sounds by comparing the input of both ears. While you can have phantom imaging directly to your sides, it's not very stable because you're essentially using a single ear (the one on the other side of your head isn't helping much).

The solution to having stable imaging directly to your sides is to simply place speakers directly to your sides. (See, I like the KISS method too.) You can be sitting anywhere on your couch, but those sounds will always be coming from your sides.

However, as Kevin explained, this leaves a hole behind the listener. Again, the simple solution is to place speakers there to lock in sounds behind you. Think of it like you do the centre channel up front; you can be anywhere in the room and you'll always hear the dialogue coming from the same direction you see the actors. Personally, I like having that sort of stability in the soundstage. YMMV. I certainly hope so. Just as you've done, I'll accomodate however many speakers I'm comfortable with and stop there.

Whatever the number of channels the future brings, you can be sure that it will be backwards compatible with existing speaker set-ups. For example: every DVD player can output 2-channels of sound irrespective of the number of discrete channels in the source material, from mono to full 5.1. So if you had never gone beyond a 2-speaker set-up, you could still enjoy discrete 5.1 soundtracks. The same will be true of additional channels and folks that have 5.1 set-ups.

Finally, I want to echo what Kevin said about having 360 degrees of sound around us. I tend to think of the four wall of a home theatre as cardinal vectors: left, right, front, back. To that end, we have the front wall fairly well covered: three speakers dedicated to the front soundstage (understandable, since our hearing acuity is at its best up front). With a 5.1 set-up, that leaves us with only two speakers to cover the remaining three walls. And that may be fine for most people, but I hope you understand that I can't really see two speakers providing stable imaging and wrap-around envelopment in all those directions.

Best,
Sanjay