800x600 is just dreadful

I agree but I don't think it's the user's `fault` if they've chosen a resolution that seems to work for them most of the time but doesn't work for your game. The user does not necessarily know what is in their own best interests. If they buy your game and expect it to look and play correctly but it's all warped and squished, even if they prefer that for their desktop, they're probably going to blame you. You should still provide the option or assistance for getting the game to look how it was intended. That said, what you intend for the user and what they do to override your intentions is largely out of our hands - but at least the option should be there.