As I recall (and this knowledge dates back to 1997 or so, so could well be obsolete), Perl does a full GC run at process exit time. In normal contexts this is irrelevant; I believe the justification was to clean up resources used by an embedded interpreter.
Embedded interpreters may do this, but the "main" interpreter may still not do this. The only time the "main" interpreter would benefit from this is if there are external resources that otherwise don't get cleaned up when the process exits (e.g. temp files).
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)