It's sort of a cultural thing amongst a lot of Microsoft employees, especially older ones (or in this case, ones that have returned), to run their blogs off of Microsoft's blogging platforms.

In this regard, Microsoft's culture actually does a very good job of encouraging its employees to blog from the inside - I've never felt quite the level of direct engineer access and communication working on Google platforms as I have on MS platforms, even in cases where Google's platforms are actually superior. (Chalk it up to Google groups being a little opaque and Google product blogs being run by product managers.)