Microsoft and its advocates have been able to say: "with a PC, you get the most choice of software and peripherals." Now a case could be made that the most choice is to be found on a Mac or Linux box virtualizing Windows on the side. The big impediment to this world is the cost of Windows, but an OEM price on the low-end of Windows could eliminate that impediment quickly.
Until Steve Jobs allows the virtualization of the Mac OS, which will happen precisely never, Microsoft's commodity cash cow could find itself virtualized into the corner.
(from Ars Technica.)
While there are always a few programs that one might want from the platform you don't have, I've found that the number of PC programs that I wish I could run but can't has waned in the past three years (since i made the switch). So yeah, I think its fair that MS has something to be afraid of.
Having said that, when I go up to an intel mac, I can't really see wanting to run windows in VM, ubuntu maybe (but all of the cool linux-y goodness is something that you more or less get in OS X anyway, so whatever).