Windows minus anti-virus

Slashdot is running a story on a statement the outgoing president of MS where he says that he's comfortable with his son running Vista without an anti-virus program running. Given MS's history with security most would scoff at this comment, but my question is with this sort of triumphalistic statement how long until Vista is the security nightmare that XP has been (surely the Windows XPerience has been anything but enjoyable for millions of users that were infected by viruses resulting from holes unpatched for months at a time)? This does explain to some extent the new stuff in the EULA limiting the use of anti-virus software. From my very biased point of view this could only be a boon for Mac OS X - which as far as I know is still as solid as a rock with few if any working viruses.