[thothamon]

I agree with your point about the time scale, but OS 9 and OS X are entirely different OSes with basically nothing in common but the name "Mac OS". It's more like releasing an entirely new OS, not shifting an OS by 180 degrees. Maybe the difference between DOS and NT is a similar comparison.

At any rate, if having a program run unchanged for the longest period of time is our gold standard, then I think MS wins. They have harmed their platform significantly by their total dedication to backward compatibility. By comparison, Apple has emphasized the quality of the platform at the expense of convenience to developers. I think Apple made the better choice for consumers (and even for developers in the long run), but it's certainly arguable.