Found this thread on their forums:

Refresh rate thread

This is not good news. 60hz gives me a headache to and makes the screen apear to flicker. I do have a refresh rate fix on my computer since Microsoft screwed up the refresh rates in XP and 2k for a number of video cards including XP. You can set your refresh rate in the OS to, say, 85hz but run a game or anything that uses 3d accelerated graphics and check your monitor readout if you can't tell but it is running at 60hz. This affects all Geforce cards with all drivers and Radeon cards I have heard, others as well. Microsoft has not lifted a finger to do anything about it.

The problem is with the Multiplayer demo the refresh rate fix tools we use are crashing the game and the multiplayer demo has no way to set the refresh rate in the game that works. So users of XP are forced to unistall the refresh rate tools and play the game at 60hz. This sucks to me, I realy hope a patch is released soon to fix that or the other tool they mentioned in the thread that *may* work. If not I won't be playing the game to get headaches until it gets resolved.

I am certain that this will not be the case with the final release since it affects far too many users. The Single player demo does not have this problem so it will probably get fixed soon, just hope it is real soon.