WordPress Themes and the GPL

There's some debate over whether WordPress themes are automatically GPL because of the way they are loaded by, integrate with, and depend on WordPress, which is GPL.

So what's the legality around creating a new publishing platform that uses the same WordPress function names (but none of the WordPress code), effectively making it compatible with WordPress themes?

What if I already had written a publishing platform in the public domain, using different function names for themes, then wrote a compatibility layer so that someone could drop WordPress themes into my application? What if someone then wrote a theme intending it for my application and its compatibility layer, and WordPress compatibility was not a consideration for that developer? The theme would work in WordPress, but would not require WordPress in order to function.

I believe in open source and the GPL. I don't believe you should shove it down peoples' throats. Yes, the WordPress developers have put a lot of time and effort into creating this code base with the intention of it being open source. Obviously the Thesis folks shouldn't have copied code, but don't let that muddy the discussion: WordPress takes a lot of effort, but so does theme and plugin development. A commercial theme does not diminish the open source foundation it sits upon, nor does it make that foundation any less open.