Peter,Man, what is the problem here - the S2 has a fixed frame size because it does not have a removable back and so a 70mm will always stay a 70mm (speak looks like a 50mm in 35 format). And this will stay like that!
So the big advantage is that you will get used to the new focal lenghts of the S system :thumbup:
I really never saw this as an issue at all. Like your comment, you just set yourself up to shoot the S system and be done with it. One of the bigger hassles I read about is folks trying to fit other glass to their differing backs and systems. Even Hasselblad has some caveats on things. So in my mind, with the fixed sensor size of the S2, you do just accommodate your shooting to work within its system of available glass. This was never an issue with 35mm either. Only became a "problem" when the APS-C and APS-H sensors were introduced, and folks had to deal with EF-S, DX and whatever other glass they needed to achieve what they wanted. As long as there is only one sensors size, it makes getting used to things so much more simple.
LJ