NumPy contains no Fortran code, and can be compiled without a Fortran compiler. What NumPy does provide is f2py, which is used to compile SciPy, which does have Fortran code.
I have found on this page: http://docs.scipy.org/doc/numpy/user/install.html following quote: "Various NumPy modules use FORTRAN 77 libraries, so you’ll also need a FORTRAN 77 compiler installed." And, on the same page: "NumPy does not require any external linear algebra libraries to be installed. However, if these are available, NumPy’s setup script can detect them and use them for building. A number of different LAPACK library setups can be used, including optimized LAPACK libraries such as ATLAS, MKL or the Accelerate/vecLib framework on OS X." The linear algebra libraries mentioned are obviously Fortran libraries. So, it seems like I was wrong saying that Numpy modules are written in Fortran, but it's still not clear to me if only SciPy modules are the ones which call Fortran libs. I will delete my comment above, anyway.
LAPACK and BLAS have many implementations, some of which are written in Fortran, but as you've said external LAPACK and BLAS libraries are not necessary to successfully compile NumPy, though they do accelerate certain NumPy routines.
