That's exactly why. It's an unwritten rule in mame that you don't emulate games that are still in the arcade. Well, there are exceptions, but usually it's because the system is so complex and processor intensive that even if they start work on it now, it could be several years before it's playable.
Misfit mame doesn't seem to have as strict a moral code. The best example I could give is D2K (Donkey Kong 2) which isn't in mame because it's so new and yet is already in misfit mame. Of course I've always found that one silly because the guy is stealing code and graphics from nintendo and making a profit from it, so who cares if we cut into his profit margin, but to each his own.