Being MS, one can promote the standards that benefit MS, whilst ignoring others. MS has decided that it will go with the latest [link|http://blogs.msdn.com/mfussell/archive/2004/05/13/130969.aspx|XQuery but not XSLT 2.0 and XPath]. Mostly I think it's a case of being arbitrary and capricious (a term quite familiar in antritrust cases btw). There are overlaps between the three, but they are geared towards different things - hammers and screwdrivers as Admin is like to say.