Python searches the paths in sys.path
in order (see http://docs.python.org/tutorial/modules.html#the-module-search-path). easy_install changes this list directly (see the last line in your easy-install.pth file):
import sys; new=sys.path[sys.__plen:]; del sys.path[sys.__plen:]; p=getattr(sys,'__egginsert',0); sys.path[p:p]=new; sys.__egginsert = p+len(new)
This basically takes whatever directories are added and inserts them at the beginning of the list.
Also see Eggs in path before PYTHONPATH environment variable.