cat, that's an option. if you go into your profile, under "look and layout", you'll see where you can deselect that, and it will show the oldest posts first in the thread listings instead.
Say you have free wireless at some college and lets say five people from that college use the free wireless...those posters will all show up as the same IP. So if one of those five is a troll and they ban the IP the other four won't be able to post.
Here's the other part...what if the IP has a Fantasy Team or League and is a Troll on CBS? If they ban the IP that Troll can't manage their team or league.