The whole driver situation will turn it into a royal PITA for CDP and given their size (while big they hardly have the recourses EA/Ubi/Activision do) I couldn't fault them I they didn't try. Witcher 2's approach to technology was so different it felt a bit like the Crysis of its time.
Why? With Nvidia Linux is faster than Windows in commercial games. Furthermore, if it's working on OS X it will work far better on Linux with proprietary drivers.