Kernel is strategically, the most important part however especially for a vendor relying on services as the revenue stream. Red Hat is the leading contributor to the core components like Kernel, Xorg etc and that is much more compared to other niche upstream projects even among those included in Red Hat Enterprise Linux. However I don't think a user space comparison would look very different either considering that some of them are covered by Greg KH already. If someone wants to run similar stats from the desktop perspective against say the whole of GNOME, that would be pretty interesting. Maybe LWN can do that?