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To answer your question, Lee has said that they will be doing this. AppGameKit uses Code::Blocks as an IDE that can be used on MacOS X and that they just have to write the compiler for mac and it would be all good to go. This is in the future, there is a lot being worked on at the moment, so we won't see this right away.
Just like Monkey, not everything is available on day one, it's going to take time to build everything that is needed. The good news is that by February 2012 AppGameKit will be six months in after launch and it's already more complete in features than Monkey.