I've read several diary posts about how this is evidence that Bush is on the run, because (even though he's unopposed) he's giving up that advantage and playing to his base.
I remember (but cannot find a link to, sorry) reading that Rove sees the country as truly divided. He believes the swing vote is going to be too small this time. So the GOP is focussing on GOTV.
In that scenario, playing to the base is vital. This is just the next step in the existing plan, not any big change.