I wish more free software developers would pay the $99 tithe to get their stuff added to the Mac App Store though. (Any free software guys here? I'll pay the $99 for the first one to email me at [email protected])
http://www.fsf.org/blogs/licensing/more-about-the-app-store-...
Now although the situation might be the same, I'm not definitely sure that it is - for one thing OSX still lets you run unsigned binaries (and thus modification to source code).
https://adium.im/pipermail/devel_adium.im/2011-January/00797...
The better answer to this question is probably that Mac OS X is not the best platform to run free software on, just like Microsoft Windows is suboptimal at best. Given that those platforms are closed and proprietary this is not that surprising. If you want to run free software, start at the bottom - the kernel. It is not like there is a dearth of choice when it comes to running free kernels after all.