I think we are all agreed that if a group chooses a name that has some indication as to the type of music they might be expected to play, and it turns out that they don't play that type of music at all, then anyone going to see them or buying one of their CDs without checking them out first would feel aggrieved.

But:

1. Caveat emptor applies - if you don't find out more about an artist or band before going to see them, it's your fault if you don't like what they do.

2. Whether you like it or not, there's nothing illegal about this.

Would you like the government to licence band names like they do with cars? I wouldn't.