I agree. But we're talking about software as a service here, and that kinda makes it a different ballgame. Folks are paying money (in some cases) to use your software living on your servers (or, at least servers that you manage). I would certainly hope that someone who can deal with outages or penetrations is actually working on the weekend (perhaps that person doesn't work Monday and Tuesday?).

Would you say "eh, but it was the weekend" if an attacker purged your paid enterprise repo on a Sunday morning?