So let's take MS's claims of a more secure Windows at face value.
This means two things. First of all, the Windows they released to the market is unnecessarily insecure, and MS knows that.
Secondly, why would they only offer this enhanced security to the Chinese, and not to the rest of the world?
All software ought to be as secure as possible. If there are security enhancements available, a vendor ought to roll them out to all their users. Here MS is failing in both: Windows can be (much) more secure than it is, and they're not releasing this improvement to the rest of their users.
That, or MS is lying through their teeth to get into China. That may be possible, but while you can say a lot of bad things about the Chinese government, their people by and large are definitely not stupid so there has to be at least some weight to the claims of MS.