this happens in evbery genre, especially the more limited ones. anything from blues to punk to house. there are only so many things you can do with the simple structure a lot of these genres consist of. if you do prog metal for example there are more different things you can try, but in the end it'll be the same.
that said, all these genres are still alive and kicking, also because new generations of fans show up that dont know all the classics, and much is new for them. and a lot of people just like to hear certain music, whether its new and exciting or not. a genre like metal is a good example of that.
but yes, i agree on house, techno, chicago, etc. too much of the same shit.
ray: as far as genre hopping goes, the story above also goes for producers. i switched in the 90's from acid to electro because the 303 was really starting to bore me, and i wont do any electro tracks for a while at least any more either because of the same reason. sometimes its good as a producer to take a fresh new road. for the last few years i've been trying to capture the feeling and darkness of old industrial and wave and incorporate it into my tracks, in the end i think its only combinations of genres that can produce anything new and fresh today.