I think that this "Mac security" thing is a myth. They are not intrinsically more secure, it is just that there are fewer of them, so it is "security through obscurity" which cannot be relied upon.

The processor has nothing to do with security, as already stated, unless the malware is ASM based, in which case some will not run on some processors.

I think that we have to see what kind of market penetration it achieves? If there is a significant increase in machines that solely boot Mac OS then that will decrease the obscurity factor. However, I suspect that a lot will dual boot, which would suggest that the traditional Windows attack vectors will continue to be used.

I really don't anticipate a massive shift to PCs running the Mac OS as it is not significantly cheaper than Windows. I really think that if OS cost is the factor people would go for Linux.

Anyway, the real reason for the price difference between an Apple and a PC is Apple's pricing and marketing policy. They could actually do themselves some serious damage with this venture?