Yes, you defined a "stroke". But you stopped there. Why?
Rule 14-1 states:
14-1. Ball to be Fairly Struck At
The ball must be fairly struck at with the head of the club and must not be pushed, scraped or spooned.
The definition of "fairly" is stated nowhere in the rules, requiring interpretation. It's been interpreted whenever required throughout golf history (banning of the croquet stroke, etc). The "new rule" isn't a "new rule" so much as it's a specific interpretation of "fairly struck at" as near as I can tell.
The fact that the word "fairly" is in there, and they didn't just say "struck at", tells me that there's more to it than just to say "you have to hit the ball with the club."
Furthermore, the definition is even up to interpretation because "forward movement of the club" can be deemed to mean more than simply "forward movement of the clubHEAD" (which is the primary reason that anchored putting doesn't fit the definition, from what I understand)
So yes, it is already in the rules. It is a precise interpretation that they're putting into a specific prohibition just to make sure that nobody else misinterprets it, as the anchored putters have been doing for decades.
"Fairly" as you stated is subject to interpretation and until the most recent interpretation / ruling anchored putting was determined to meet the criteria and does not according to current version of The Rules of Golf violate that criteria and won't until 2016.
Also be aware that anchoring will still be allowed after 2016, just not against the body, as described by the USGA. In the "Long Putter Not Anchored" example , the club head would be the only part of the club moving forward, the handle is anchored in the hand that does not have contact with the body.