(And actually: mxCrypto is the most capable of these packages and might be the one with the most users, but it's completely unsuitable for the core because of its size).
mxCrypto is primarily unsuitable for the core because Marc-Andre Lemburg will never ever contribute it. He is very concerned about including crypto code with the Python distribution, so he certainly won't contribute his own.
Regards, Martin -- http://mail.python.org/mailman/listinfo/python-list