The release of free TF2 actually made me realize how there may never be a TF3 -- or at least, not for many, many years. There's little reason to. The gameplay is very good and the engine they are running on is in no way a limiting factor.
The only thing TF3 would have to offer is graphics, and with TF2's "cartoonish" style, I have to wonder what there really is to improve upon there.
But jQuery is a library, not a programming language. A web developer should not depend on jQuery precisely because it is not available in every javascript environment.