Actually this seems to be more like the artificial cap that sony introduced on their playstation portable gaming system. By "under-clocking" the cpu nokia was able to establish the current battery time/cpu cycles we find in OS 2007. Now that they are introducing OS 2008 which is most likely better optimized they can remove this cap on the Nokia n800 and run it at it's factory default speed. This is all speculation of course until we get a definite answer but it does seem the processors are the EXACT same.

Edit: Yep seems that's the case the cpu in the N800 and N810 are exactly the same and the 400mhz will be unlocked in os 2008 for the N800 model. *confirmed by one of the Manager's on Jaiku