[ohkine]

First of all i don't think Apple has done that bad with backwards-compatibility. The jump from OS 9 to OS X was extremely easy thanks to Classic and Carbon support, and then the jump from PPC to Intel was easy because of Rosetta. But admittedly this is not on the same level as being able to run 16-bit Windows 3.1 applications on Windows 7.

That said:

Microsoft's backwards-compatibility policies are great for businesses, who naturally have many special considerations when it comes to legacy applications.

Apple's policies, on the other hand, seem to be more geared towards improving the experience for the user. They deprecate libraries and functions of the OS that are no longer relevant to how computing gets done (or how they want it to get done) on the Mac. This helps to ensure that applications keep up with the times.

Microsoft don't have this philosophy at all, and so Windows 7 often feels like an arbitrary mash-up of the last 25 years of PC operating systems. There are many many applications in W7, for example, where buttons and interface elements still have a Windows 95-ish feel to them, because they haven't been updated to the new system themes. A famous example in Vista (corrected now in W7) was the 'Add Font' dialogue, which had been exactly the same since Windows 3.1. Another example is mIRC, where (if i remember right) some decades-old Unicode work-around forces the application to use non-Aero title bars.

At the risk of sounding like a snob, the whole experience -- to a consumer who appreciates good user interfaces -- just feels kind of amateur-ish, really.