It must have been a while since you last checked. Many of the features listed here as banned because of lack of VisualStudio support have been available in gcc and clang for years.
Not everyone has the most recent versions of the compilers, either; my institution is still working on the upgrade path from Ubuntu 12.04 LTS to 14.04 LTS, so I had to get a modern gcc manually compiled to get proper C++11 support, because nothing in the 12.04 package manager had full support.
http://blogs.msdn.com/b/vcblog/archive/2014/08/21/c-11-14-fe...
Last time I checked, outside most C++ compilers were still catching up with C++11.
There are more C++ compilers out there than just clang and gcc. Even those aren't 100% compliant at library level, if I am not mistaken.