This may sound silly, but I think it's the language barrier.

Also, Matz has been very loyal to the core group of Ruby maintainers even after Ruby has gone beyond fad status. Matz has been reluctant to put Ruby on a distributed SCM as well.

I expect all of these issues to be resolved within the next few years...

I think you're right about the language barrier.

Also, I don't really care if these community enhancements make it to the "proper" Ruby or not. The main thing is that it is available to the community, whether christened as the "Matz" Ruby or not.

true, but it's just a pain to use someone's nonstandard fork of ruby... there are a lot of awesome ones on github already, though, and I recently noticed that the latest version of ruby enterprise edition has rolled in a few of the better known ones.