It is much easier to design and build an OS / drivers when you control every bit of hardware in the system - OSX is fine but it is hardly an open OS.
I'm not sure what the rave about bootcamp is - It is really just a hack to get past EFI BIOS. From there out you are actually all MS working on apple hardware... MS should get the credit! They allow there software to run on Apple... Try OSX on a Dell.
I know MS is a big company and has its challenges but in general they've hit the mark with the software...
IIRC the research shows Vista has had less security defects than OSX...
http://blogs.zdnet.com/security/?p=758&tag=rbxccnbzd1
PS I have a PC's and a mini mac which is my media PC connected to my PC. In the last 2 years I've had to rebuild from install disk the Mac twice the PC never. My PC scarily has been rather stable under Vista 64 - The only crashes have been memory errors due to very tight timings and a heavy overclock.