Microsoft's defaults seem to fall into one of three (well, maybe four) categories:
1. Ooooh, look! New! Shiny! We just *know* you will love this.
2. Our advertisers and/or marketing people have requested us to [enable | disable] this by default.
3. This is the way it's going to be [e.g.: "The Ribbon"]
4. Because it's the only sensible default [have not seen this since XP]