Technically, yeah perhaps that's fair enough. However, your card continues to work like it has, it doesn't suddenly start performing worse, and if anything, you now know what to look for (bring that memory use down a little) if you should run into sudden performance problems. Not a massive sacrifice by any stretch of the imagination.
So really, if you want a refund because of "wrong specs" you're really looking for a way out because you may have thought you got more than you did, but technically really only on paper. Performance hasn't changed.
Good chance it'll affect future purchases though.