Well, the minis have used mobile versions of the "Core" CPUs in the past, and the "P" (25W TDP, 3M cache) and "SP" series (like "P" but socket-less, 6M cache) were only recently released to accompany the "Centrino 2" platform. There's even a quad-core mobile Core2 out. (except it's got a TDP of 45W, so calling it "mobile" is a stretch) On the desktop side, the Nehalems (Core i7) are brand new.

I doubt they're waiting for yet another iteration.