Given the frequency with which Ubuntu pushes updates (every couple of days it seems) and that handling these updates requires an administrative password, I can see sound user experience concerns which Android would better address.
Even with that though, the kernel not getting updates and continued patches makes it harder to keep things built for an end user, but I'm not sure if that is so much of an issue past the Linux 2.x to 3.0 jump with Android devices.
Updates for anything Android outside of Nexus devices that Google maintains are generally far from automatic or dependable.