iPhone Missing Features, Hardware, and Software

Most of the problems and lacking features with the iPhone can be entirely solved with software. Except for a real keyboard, there isn't much that I really miss when it comes to the iPhone hardware. The question is: as Apple fixes their software and adds new features, will new versions of the software run on old iPhones after new models come out?

This is how it is with Mac OS X. Doing the same for a phone would be quite a shift in the industry, and if one company can do it, it will have to be Apple. But will they have the guts to make a move that can hurt their sales of new iPhones models in the short term to make their platform stronger?