Personally I don't like the double standards with wp.org.
Themes get to have a "non" removable credit link. Those that do commercial themes can be listed.
Plugins have to have a optional credit link which must be off by default. We will probably never see a commercial plugin section.

Personally I think its all bullcrap. Neither themes or plugins should have credit links on by default.
There is that moronic statement that users can remove the credit link from the themes themselves.
I don't think most can do that or know that they are allowed to. Heck even if they do it, the link will be reinstated with the next theme update.