WordPress.com doesn’t like Google
http://faq.wordpress.com/2005/12/08/adsense/
Apparently WordPress.com doesn’t allow its users to place ad’s on its pages, which begs the question; why not?
WP.com doesn’t lose any money from user advertisements, and the server load from Text ad’s are basically negligible.
This is very annoying.
But apparently there are adds on WordPress.com. The thing is that you don’t get to have any money from it. It all goes to the guys at WordPress.com
If you want to keep track of more of the insanity that is WordPress.com you should check out http://wank.wordpress.com/ which kind of keeps tweeking the noses of (if not beating their heads in) the wordpress people for their annoying stuff.