I doubt this will help Apple sales, they're too expensive here, and must be astronomical in China. The iphones were made just outside of Hong Kong, then shipped to Cupertino for Apple to "inspect". They were sold here for $400, then some of them were shipped BACK to China and sold for $500-$600 - American! If their PCs follow suit, there is no way Macs will benefit from anything short of a MAJOR Windows price gouge (even more than Vista's prices, like say twice). I think Apple sells tons of ipods in China, but probably not too many Macs.
Remember that China has their own state-sponsored Linux distribution called "Red Flag" which they offer, not for free, but very very very cheap. Red Flag is essentially an XP clone as far as the GUI. Anyone caught using pirated versions of Windows is given the option of purchasing a legit license or going with Red Flag to avoid fines, jail, etc. But it's been reported that even those with legit copies are being hassled to go with Red Flag. By developing Green Dam only for Windows, the government could be trying to push MS out of China by making the Windows experience even more of a hassle than it already is - EU style.
Whatever the reason behind it, I hope the Chinese people find 1,001 ways around Green Dam, whether within Windows or elsewhere. I hope they make blocking/filtering/censoring the web the biggest PITA losing proposition the Chinese government has ever dealt with. The issue of net-neutrality is more important than any OS war.