Just go more in-depth for that, its not because its not optimized for the computer its not optimized for your computers build, IE hardware. As a game developer its incredibly hard to make your games work well on every type of setup.
It's not a problem that I care much about.
Yes, there is the argument that not every computer is optimised to play it however it's the game developer's priority to ensure a good gameplay experience. To have lag is to have failure on the side of the developers.
(best example is Ship sim Ex)
Anyway
I'm not sure about the performance with two 6870s if you want I can give you a 3DMark result or my Windows 7 score which is 7.5 out of 7.9