Upload & Sell: Off
From what I understand, as of about 3-4 years ago, Mac's run on the exact same hardware platform as PCs. They used to use RISC chips that OS/2 would run on, but now they use the same.
Instead of the Windows platform pulling drivers for the components used, Apple's OS integrates the hardware code needed.
So as others have mentioned, it's Apple's control of the platform. Which has it's pluses and minuses. Plus being ensured operability as they don't have to sign you up to the driver of the month club and find out one month's driver set you back. A minus is with Apple's finite control and pre-integration is they set the platform definition and therefore the price.
Overall the user experience is about using the computer - not supporting it...another plus! But this convenience comes at a price premium.
On the software front, again, Apple has a more stringent process of certification that a program will work with their OS (hardware and software components).
Then there is market share - PCs still dominate over Macs by at least 5:1, so as a programmer, who would you want to program for? There is plenty of software on PCs that Mac users would like to run, but there is quite limited titles that PC users feel the need for. So while Apple has OS restrictions in place of working on a 'non-standard' PC, there is just simply limited market for such a demand.
Personally, I'd love to see FCP for PC, but that's probably not going to happen. Luckily, there are tons of other options for PC that can fill it's place.