GCC 4.7 (via brew) keeps including from "/usr/include/c++/4.2.1"
that note just refers to the 4 libraries gmp, mpfr, libmpc, ppl and I think means that if you use these they need to be before the standard search path.

Your issue is where is the compiler looking for standard library headers (and later libraries). gcc defaults to /usr/include which is installed for Apple's compilers and that gets redirected by version to the path you see.

You need to explicitly set the paths to look in the hombrew compilers path first