They haven't decided to pull out completely from China yet. They simply said they might, and their main focus was to stop censoring as much as they can "within the law".
I am really surprised that you have been voted so highly as though you and many other readers here mistakenly interpreted this as an absolute sign that Google is going to withdraw from China.
"[...] over the next few weeks we will be discussing with the Chinese government the basis on which we could operate an unfiltered search engine within the law, if at all."
They talk of filtering as an all-or-nothing concept. They want to operate unfiltered search (not semi-filtered, or filtered to the extent of the law). "Within the law" refers to the fact that they want to accomplish unfiltered search in a manner that is legal and their statement is rather clear that failing that they will be shutting down.
You're right, though, that this being an ultimatum isn't stated in clear (binding) legalese—quintessentially their wording of "not willing to continue" instead of "will not continue". This is almost certainly intentional.
However, it is a press release that declares intent, generates expectations and has a common and obvious interpretation as a take-it-or-leave-it deal. From a public relations standpoint, Google would not benefit from doing something completely different.
Just because you think it is sure sign that Google will withdraw does not mean that they will. So far this is nothing more than an empty threat.