If you are referring to:
The Airstream List
that's the Airstream List, now on Yahoo. It's a good group that's been around for awhile and I enjoy both it and this site.
An email list has the advantage of downloading all your mail to your PC quckly, letting you read it off-line, compose replies off-line, and then upload those next time you check mail.
This isn't a big deal if you're constantly hooked up to a phone or data line, but if you're on the road, borrowing phone lines or even accessing the net over a 9.6 or 14.4K cell phone, the last thing you want to do is use a web browser!
The Yahoo "Groups" which came from eGroups which came from oneList, also let you specify to receive plain text rather than HTML mail, to keep things quick.
Let me correct some misinformation you posted:
"The messages are posted in just one long continuous thread"
If you subscribe to an email "digest" you'll get all the messages for a certain time period in one long message. If you subscribe in "list" mode, you'll get each post as an individual email. If you view it on the web interface, you access each message individually, not in one continuous thread, but you'll have to put up with a full page Yahoo advertisement about every third screen and a Yahoo ad in each message.
"each message has to be approved by a moderator before it is posted. "
Wrong. The FIRST messages of each new user are moderated. Usually only the very first. This prevents advertisers and spammers from joining the list, posting an ad, and disappearing forever, as they do in unmoderated groups.
Let me also add, the Airstream List "Group" doesn't permit attachments, which prevents you from getting email viruses from them.
If I may say so, you didn't bother to gather enough information about it, or gather it correctly, to be criticizing it here.