True. We all assume that every company computer has a legal copy of WinXP. I would bet that's not the case. What if that's a company you gave credit card or personal information to. They will not have the SP2 security update and you know the rest of the story. Not to mention all the bad news about security problems with Windows will not likely fade, like Zone-MR has pointed out above.
But of course this is nothing Microsoft has not already thought about.
This actually matches up quite nicely to the initial reports, because they quoted Microsoft group product manager Barry Goffe as saying Microsoft had not "explicitly done anything to SP2 to exclude it from pirated copies", and that: "It was a tough choice, but we finally decided that even if someone has pirated copy of Windows, it is more important to keep him safe than it is to be concerned about the revenue issue... Having these unsecured users means bigger worm and virus outbreaks - which also impacts the Internet and consequently, our legitimate users as well."
...this is why they are known as M$ :P
http://www.theregister.com/2004/05/11/xpsp2_pirate_blocking/