Microsoft has a tradition of dogfooding -- or testing internally -- the stuff it develops before anyone else gets their hands on it. For example, Puhl also notes that Microsoft is testing its forthcoming master data management product, despite the fact that it won't be released until the next version of Office gets shipped.
The few things that we know for sure about Windows 7 are that it will have multitouch support and there will be some changes to the taskbar. We don't even know that much about Windows 7 Server. With Windows Server 2008 generally getting positive reviews, what should Microsoft add or tweak in the next generation? Who knows, maybe we'll hear more in the fall.