Whatever dude, Red Hat and Novell (-> SUSE -> Ximian) got there first. It's the same reason recent pickups at Intel's OSDL largely Red Hat ex-employees. If you wanted to do work in Gnome or Linux back in the day and still get paid, there were basically only two games in town.
It isn't a good or bad thing, it just is. And we can't expect upstarts like Canonical or Intel to be there just yet. It's just an observation that a lot of Gnome developers cut their teeth at Red Hat before moving on.