nvidia has made a lot of workarounds around xorg-server to have their drivers work the way nvidia wants. that was just one of them.
i think it's only natural that xorg team considered nvidia's behavior a bit too invasive, and perhaps dangerous for people running unstable X snapshots. still there could be more reasonable solution to the problem, but unfortunately nothing good comes to mind.
haven't tried radeonhd, but xf86-video-ati works like a charm for me, thank you. i tried fglrx yesterday and my pc totally locks up after 2 minutes of watching video (regardless of resolution/codec/format/player).I mean hey you can always run RadeonHD without issues can't you?