I am sure there is good reason to combine and make systems and games indistinguishable and I will always respect the ideology, politics and direction of MAME even if I don't agree with it.
Having said that, it can only be a five minute job for any coder to add another variable and I think some of the derivative builds are already starting to do it. If not I expect they will.
To comment on what RBelmont said, they are not going to see the work anyway if a utility or front end expects to see or list a MAME game. The user will just see the name of the system that won't launch or work.
Anyway, I can't see that this won't be addressed in a future release. I am sure it is not a big deal really. Probably just more of an oversight.