There have been no updates for xorg-x11-drv-ati in Fedora 13 since its release. And yet I read about various patches and improvements being made at the developer level. Does this mean there are some complicated dependencies which inhibit update releases, or is it just that the Fedora folks are asleep at the wheel?
Fedora is not known for its post-release improvements. You pretty much have Rawhide, which is more or less always containing the latest version of every FOSS package that goes into Fedora; and then you have the releases, which rarely see any work short of security updates -- and even those only last a very short time compared to other distros.
On the other hand, RHEL and CentOS are famous for being a combination of old, crusty code and backported fixes and applications. CentOS 5.0 was released with Firefox 1.5, but CentOS 5.5 (and similarly RHEL 5.5) ships Firefox 3.0.18, which is much newer.
That's not to say everything in RHEL/CentOS 5.5 is shiny new, but a few key things got backported safely, including new hardware support for the ancient 2.6.18 kernel.
I think Ubuntu is heading in a direction where they will provide more robust stable updates. But I don't think even Canonical is brave enough to upgrade the open source graphics stack post-release; this can (and very often does) break some hardware while fixing others. The last thing they want is regressions on their hands, so they'd rather let the people for whom things aren't working, suffer (or upgrade to a new release).
Bottom line, if you want a constant stream of updates, use Fedora Rawhide, Debian Unstable, or ArchLinux.
Make sure you have fedora-updates repo on. If you want to live on the edge, fedora-updates-testing is for those who don't care if their dependency trees break. Then again, git installs of newer display drivers usually work just fine with Fedora components since prerequisites are new enough.