Apparently it was discovered and raised as an exploit, never patched, and never used until today? It makes me wonder how many other known unpatched exploits like this are out in the tall grass.

It looks like it was patched (as far as I can tell): https://technet.microsoft.com/en-us/library/security/ms14-06...

Is the problem that many people in China are using XP, or pirated versions of windows that don't get updates?