@Bass: Why the surprise? When XP was released (2001) nobody had it enabled by default. Since that's a heck of a breaking change, it's not something you can do safely in a service pack and it had to wait until Vista. Incidentally, Linux managed to do so only in 2004, so - again - I don't understand the surprise.
What's sad is that there is still a cartload of networking gear that don't implement RFC 1323 or are not configured correctly. And since the standard response is "oh, that's a Vista bug, type this netsh command to disable the bugger", things are improving a lot slower than they should.