You'd be insane to develop something of the complexity of Stuxnet and not include a full end to end test in the QA process. It would be incredibly embarrassing for this to fail.

You don't really need the centrifuge, just the inverter.

I was working in industrial control and automation at the time, there were sweeping changes to what could and could not be done and by whom at every level.

Old drives of all manufacturers that sat unused were audited and had to be brought up-to-date before any sale or change of hands could occur, serials were noted etc etc.

Never felt like a manufacturer decision since it occurred in unison almost globally.