It shouldn't be a problem if they made it scalable. Apple does add features that the previous iPhone doesn't have (e.g. digital compass). It just takes developers a while to target the newer hardware since they want to maximize profit by hitting as many targets as possible (e.g. lowest common denominator in hardware).

As for obsolete, it depends on how the company supports their product. For example, I believe Google is still trying to get 2.0 on the G1. It may take advantage of all the benefits 2.0 can provide due to old hardware but you can still have the latest optimizations, fixes, whatever. On the hardware front there's nothing you can do, it's just the nature of technological advance. It's on the software front that matters.

Likewise we'll see how Nokia handles it. Or if it'll be one of those "fixed in fremantle" things but instead with "fixed in harmattan". Granted the choice of QT will allow applications to be cross-ported between Symbian, Maemo, and any device that runs QT.