Having two good compliant compilers is great for C++ too: it keeps both compilers honest and also makes spotting weird behaviour easier in big codebases (i.e. to first order if your code results in different behaviour in GCC or Clang then it could be dangerous).

Also has the added benefit of reducing the need to use compilers like Intel's (not sure on current benchmarks) but I really wouldn't want to ship something for AMD CPUs with Intel's compiler.