You get to see this at CppCon 2014 videos.
On one side, very rigid companies barely using C++11, mostly as a better C with improved type checking.
On the other side, researchers making use of every template metaprogramming trick they can remember of.
Looking at the headers is not the way to learn about the library. Anything that you learned that wasn't documented in the standard or any of the many books, articles, and videos available would be an implementation detail that you couldn't rely on in portable code or even in the next version of gcc.
These files are only intended to be seen by the compiler and it doesn't complain about indentation or single letter variables.
I feel it's even worse than that, though. There seems to be a culture among C++ programmers to do things in overly clever ways and to push the limits of readability and understandability. Just look at the headers for the standard C++ template library, for example. (I'm currently looking at the ones shipped with gcc.) They don't even use consistent indentation, and have single letter variables that are meaningless to all but those who wrote it. It's pretty frustrating to deal with.