Because Dharma is the current stable version? As far as I know, there's a few eden patches backported too - obviously not the dirty region GUI stuff though. There's always been development builds for eden available at
http://sources.openelec.tv/tmp/image/openelec-eden/ if that's what you want to run (which is what I'm running on 2 of my systems)
The nvidia (doesn't have to be ION obviously though)/AMD thing is no different than any project/software/etc though.... This is linux remember!
Saying that, I've got a zotac ad10 (amd fusion e350 based mini pc) running an openelec eden build and it works brilliantly - I've only had (macroblocks) trouble with one file.
It takes longer to type a question like this than it does to try it for yourself!
But... Unfortunately, there's no web browser included with openelec, xbmc or xbmc live.