The text wrap thing works like this:

If somebody makes a really really WIDE post by using the PRE tag and pasting a wide line of code into the message, or if they link a very large picture, then this might force the message table to be wider than your browser window. So then everyone else's text doesn't wrap right after that post.

In my opinion, each message should be its own table, instead of cells within one large table. It's possible that they deliberately did it this way because of bugs on certain browsers or something, I dunno.