I don't know why Steam games would fail too. There shouldn't be such a problem with Steam right now unless Steam is doing something or had a problem, in which case there would be news articles about it.
I've never heard of such a problem, let alone with a Radeon 6870. I'm not a huge gamer so I could have missed something like this, but I do keep up with news articles and with the graphics technology and i've not heard of this problem before.