Actually, I think there are *many* parts compiled. You can start with the python interpreter (executable). There has to be something that actually runs natively on the OS. If you look at the developer/build instructions at
python.org you'll see you need a C compiler.
In addition, NumPy/SciPy require C and Fortran compilers to build. Qt is used for the GUI toolkit, which is written in C++, so it will have to be compiled per OS as well. I expect there is more.
If you'll look at this link -
http://spyder-ide.blogspot.fr/2012/08/scientific-python-distribution-for.html - you'll see some discussion of these compiler issues Pierre had to address when he started WinPython. I think it would turn out to be a good bit of work. However, it's open source, so if you want to learn how to build all these packages for Mac...
(Hope this is all correct from Pierre's point of view.)
Jim