My guess? After you successfully login the webpage is setting a cookie
on your browser with a token to mark you as authenticated and let you
in. Lots of websites do that: I don't think urllib2 is handling that
by itself so you may need to. You also may have to set a User-agent
header to convince it you're legitimate.
I googled briefly and came up with
http://www.voidspace.org.uk/python/articles/cookielib.shtml which may
be totally useless or of great value. I am not providing it as a
solution, it just at a brief glance looks potentially relevant :)
--S