If you don't want to add a dep on numpy (which is a big complex module) then it's nice to have a stdlib option. So there are certainly at least some cases where you're not better off with numpy.
"Providing a quality implementation of matrix multiplication is highly non-trivial. Naive nested loop implementations are very slow and shipping such an implementation in CPython would just create a trap for users. But the alternative – providing a modern, competitive matrix multiply – would require that CPython link to a BLAS library, which brings a set of new complications. In particular, several popular BLAS libraries (including the one that ships by default on OS X) currently break the use of multiprocessing."