"Possibly Canonical prefers to spend its effort developing components which aren't in the rather small set Greg checked? Things the users can actually see? Things like, oh, GNOME?"
Yes, surely thats the ticket! Tell yourself whatever lies you have to, the work Ubuntu does, is for Ubuntu. If you think not... Go get the source and prove me wrong. Greg mentioned he looked at more then just the kernel but left it open enough that someone could tell themselves "Oh, they must just not work on the kernel."
I'd challenge anyone with Ubuntu/Canonical to post their own numbers _from an upstream repo_ and show where Ubuntu/Canonical commit count is at vs other distributions.