Because it is totally undefinable, and the range of bands considered as 'classic rock' speaks volumes against it being a genre. All bands considered CR are comfortably classified anyway, to call it a genre is superfluous, and the point of genres is to be concise.
It's never stupid if you ask though, rather than fighting as a lot of people do.
hahaha Thank you.
DLC Wishlist: Green Day, Cream, Sublime, The Doors, Audioslave