Binary archive includes a reference implementation blas library.

The unusual ddl directory 
  /usr/lib/lapack/cygblas-0.dll
  /usr/lib/lapack/cyglapack-0.dll

is to allow to create locally optimized lapack and blas libraries,
ATLAS (http://math-atlas.sourceforge.net/).

  /usr/bin/cygblas-0.dll
  /usr/bin/cyglapack-0.dll
and to have them in precedence on the PATH