The whole point of .cache is that it's supposed to be that one folder that you know you shouldn't back up. As opposed to a dozen different app-specific ones that we have today.
Yes, it's a great idea in principle -- and would be even better if its location were configurable, per the XDG spec.
My comment wasn't meant as a criticism of the basic idea of a standard directory scheme; it was a reply to someone asking why anyone would ever care about files you can't see.
