"Hey your systems have been vulnerable for a week; here's the patch!" just doesn't fly too well with major customers with very real needs for security.
I personally don't mind them being used in real targeted surveillance either. That surveillance is going to happen anyway.
You hear this and then, on this website, people get all incensed when China sponsors industrial espionage against US companies. What I'm saying that moral consistency is required, it makes people predictable.
Major customers with very real needs for security probably aren't running Windows... Even if they are, they should be sandboxed in such a way as to reduce potential damages from a 0-day.
Plenty of big organisations use Windows for almost everything, and certainly don't go around sandboxing it. They manage regular security patches just as you would for any other operating system. As a (perhaps extreme) example - the Royal Navy use Windows to run several of their warships: http://www.theregister.co.uk/2009/01/05/windows_for_warships...