the key is reading the readme, not just the make.osx file.
These commands Just Work: make -f make.osx PYVERSION=2.6 PREFIX=/Users/adam/repos/mpl_dependencies/ fetch deps mpl_install_stdmake -f make.osx PYVERSION=2.7 PREFIX=/Users/adam/repos/mpl_dependencies/ fetch deps mpl_install_std
while, e.g., this one: make -f make.osx PYVERSION=2.6 PREFIX=/Users/adam/repos/mpl_dependencies/ fetch deps mpl_install didn't. I guess because that one doesn't actually install anything.