IMHO monitoring/controlling a high-speed centrifuge with Windows (or with any non-real-time-OS for that mattters) is actually a huge design flaw, there is even a warning somewhere in MS documentation about Windows not being suited to Real Time operation, and RTOS are specifically used/needed for closed-loop applications (such as monitoring and controlling motors).
Ok, still seemingly the trick Stuxnet used was looping a good copy of those fancy panels and (still through windows) changing (slightly) the operating parameters of the machine, so in this case Windows (directly or indirectly) was capable of monitoring the device and change its operating status.
Are you saying that there are no zero-days for platforms other than Windows? There could just as well have been a Linux computer used as interface to the embedded system that runs the centrifuges, that could be owned.
Not really saying that, of course any OS is hackable, Linux also is not normally a RTOS with the exception of RT Linux, and possibly some other specific distro's.
What I was trying to say is that something that has a more direct connection to the device is less likely to be prone on this specific kind of attack, which is AFAICU a sort of MITM (displaying a loop of the recorded display), and of course with a very "vertical" and "dedicated" operating system there should be less chances of the "casual" insertion of a USB stick in it (and possibly even no USB port at all on the actual hardware used).
References (National Instruments):
http://www.ni.com/white-paper/3938/en/
http://www.ni.com/white-paper/14238/en/