Metal is horrid about that kind of thing, as you said. Very few classes of Metal actually deserve to have a subgenre of any kind.

The only one that comes to mind is Power Metal, which makes heavy use of orchastra Type equipment, a good example being Kamelot's Ghost Opera using organs and violins, and the over all feeling of the music differs a lot from normal Metal.

THere are other examples of legitamate sub-genres, though overall I think it's just people being elitist.