What management are you talking about here ?? It seems to me that duplicate copies of identical files (one copy per platform) is inconvenient (at least for my perspective).
Suppose a new version of a package is released for platform X but not yet for platform Y (maybe platform Y is less popular and the only maintainer is on vacation). Further suppose the platform-independent files are changed in the new version. Now if you install it in the shared area for platform X, you screw platform Y's installation. Without a shared area, each platform can update without affecting the others.
Moreover, why provide an prefix and an exec_prefix if we are going to put everything into the same tree anyway ??
They are old features; 5 years ago this was worth it to save 0.5 Mb of disk space.
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)