All of the libraries you've referenced are indeed a part of the C++11 standard. In fact, a lot of the language rules were reworked to describe how operations work in a multithreaded environment (previously, the spec didn't specify any semantics for how threads would work).
I can't say why the documentation is lacking on those sites, since I don't know who runs them, but threads, atomics, etc. are definitely a part of C++11.
On a related note, I would strongly suggest not using cplusplus.com as a reference. It's known to have had some inaccuracies in the past, and other sites (namely, cppreference.com) are a lot more complete and accurate.
Hope this helps!