Re: That's a real beginner's mistake...
Couldn't possibly agree more. To add insult to injury, most mailing-list managers have some sort of graphical administration tool (be it by web or by GUI). A few clicks, surely, is all it would've taken to put it right. Although it should've been right from the start.
Re aliases: it's damned tempting, for sure, to use aliases rather than intermediate mailing-list managers. Most MTAs even make this easy (for instance sendmail using owner-list and list to control returned mail and membership). The real advantage is speed; the MTA can optimise bulk deliveries. The disadvantage is practically everything else - filtering of any kind, moderation, MIME part stripping, bounce handling (although you could still have a custom robot for that purpose, it would be harder to use). Most obviously it means user management of subscriptions is nontrivial. Depending on mailing-list manager, speed may be impaired (those using VERP, for instance, where envelope sender is varied uniquely per recipient so that bounce handling becomes straightforward). Others do it right, though - they accept the message, then call the MTA to send en-mass after doing filtering.
Ah well, guess sysadmins don't come cheap over there.