Ya, developers should just switch OS midway through development, right?
Game studios are almost never completely done with one game before they start another. So unless they upgraded midway through development, they would never upgrade.
Development should be almost done, and they should be beta testing if they are going to be ready for a November launch.
They upgraded their PCs or at least their video card to the latest Nvidia 700 series "midway" through their development cycle. Of course a newer series of video cards is better, can't say the same thing about Windows 8.