@Andreas Nurbo - I'm fine with the way things are. I understand the difference between plugins and themes and the external link guideline. You're in the position where you will have to agree to disagree because it looks like it won't be changing anytime soon, especially after what Mark said in the forum regarding plugins and themes.

Theme credit links can be argued but I think it's one of those argue until you pass out scenarios.

All I can think of is that they needed more designs from the start and designers are more cranky about GPL etc so to accommodate them themes were given the right to have credit links.

I think of Marks answer as the core reason why themes and plugins are handled differently concerning the credit link guidelines. It has nothing to do with anything you just mentioned.

Your last question is answered by Mark, go read it :)