"The USPTO doesn't want any responses faxed - just emailed, which begs the question why that wouldn't work as a fax alternative."
Let me guess. With patents precedence matters. If the situation arises that two inventors submit similar claims at more or less the same time they need to decide who has precedence. With fax they know - transmission and reception are simultaneous. Enail is store and forwards so time of receipt is no indication of time of transmission and if that same situation arises they won't know and the loser will always claim theirs was first but delayed and/or dirty tricks were played with clock setting.
OTOH a prolonged outage of all forms of communication to USPTO wouldn't lose anything of value to humanity as a whole.