Windows XP SP2 Now Required to Get Security Updates

While it comes as no surprise to me (at least from some of the reports that I have heard) that Windows XP SP2 uptake has been slow, it is surprising that Microsoft made it official that PCs must have SP2 in order for Windows XP updates and security patches to be downloaded.  Considering the low percentage of XP machines that currently have SP2, is limiting the ability to install security patches really the way to go?  Especially this soon?  Seems you don't have a choice though, which makes me glad I don't admin 1000 corporate WinXP boxes.  The thing that strikes me as odd about SP2 is that many of the XP vulnerabilities I see seem to effect machines with SP2 installed anyway.  Once again...vendor lockin==bad.
--jeremy