I know what I'm about to say is going to make a lot of people want to bitch and moan but it is something I truly believe...
If Steve Jobs didn't come back to Apple and didn't make Mac computers SEXY machines, Apple would still have less than 3% market share right now. I truly don't believe the OS is the selling point for Apple. The OS is simple as hell and nice to use...until you need to do serious work. It's an OS that is GREAT for a child. No viruses to worry about and very simple. But for anyone who wants to get real WORK done, it just can't compete with a PC. Now Apple will continue to win market share b/c their computers look fantastic, but it's definitely NOT due to the OS.
So I guess if you were to put Windows on Macs and sell them, Apple's marketshare would suddenly jump through the roof.