Is it OK for TM2 to require GPL forks but request dual-license patches?

What I am confused about in this whole thing is because you are developing these patches and fixes and additions using the gpl code doesn't that mean that your patches cannot be released under the public domain as per the gpl because of how your code was made.

I'm thinking of this in the same way that wordpress themes/plugins have to be gpl if they use wordpress functions and such.

Wouldn't your patch have to be completely separate from textmates code to be considered eligible for anything other than being licensed as gpl?

I do not mean this to be a push-poll, I'm pretty ignorant here and just want to survey opinions. Personally I think it's the author's prerogative to release his work under whatever terms suit him as it's his work and no one is obligated to use his code or contribute to the project.