Microsoft Virtual PC 2007 SP1: Where's the Beef?

Microsoft just released...

Microsoft Virtual PC 2007 SP1

Now, it seems to me that SP1 (Service Pack 1) type releases are usually fairly significant. New features, better security, that sort of thing. But the only changes I see listed are support for the various Windows Vista and Server SP1's themselves (plus Server 2008 Standard Edition). The funny thing is that the pre-SP1 VPC 2007 worked just fine on my Vista SP1 box. So, I'm not sure what it fixes.

I would have been much more impressed if they had added support for current generation Linux/X11.org releases or better USB device support.