Then I read this and something that had been floating around in my mind began to solidify. KDE assumes a platform and attempts to work around its shortcomings. Gnome helps define the platform and works on fixing its shortcomings.
It's pretty easy to see this across the platform. The developer of the Gnome Bluetooth support has multiple commits to the underlying Bluetooth stack, while nobody who's committed to bluedevil appears to. The main developer of the Gnome Networkmanager support is Networkmanager upstream, with the same applying to the Gnome power management infrastructure. And when Gnome developers find limitations in graphics drivers, those tend to be fixed in the graphics drivers rather than worked around in the UI code. KDE builds on top of what's already there, while Gnome is happy to flatten some mountains first.
I should emphasise that I'm not criticising KDE here. These are both rational development models. One optimises for making things work and will compromise on functionality in order to be more portable to different underlying operating systems. The other optimises for additional functionality at the cost of being tied to a much smaller number of underlying operating systems that have to be completely up to date. But understanding that this distinction exists is key to understanding fundamental differences between the projects, and any argument about which is better or about how there should be more collaboration has to take these fundamentally different approaches into consideration. My personal belief is that a tightly integrated platform is going to produce a more compelling product in the long run than one built on top a series of abstraction layers, but we'll see what happens in the long run.
And then, of course, there's Unity and Canonical's gradual effort to turn Ubuntu into a platform distinct from either Gnome or KDE. But that's a separate post.
 Well, except for the melted ice cream at Akademy 2006. But I think that's fair.