It's interesting that the themes available on Wordpress.com aren't GPL licensed. This does seem a little hypocritical.
So they may say it is GPL, but in practice it's not.
It may be in the terms of the Hosting contract?
They distribute the css, in that they let us edit it, but they limit what we can do with it. Not GPL.
I think you're wrong. The GPL governs code, not services (even services that use GPL code).