To each his own, I guess. Personally, I'd much prefer a nested-type display, a la Slashdot - it just makes it easier for me to follow the flow of a post and the replies to it, and the replies to the replies. And Slashdot does give you the option of having a flat display, in chrono order, like FR does.
Although, I'd imagine that sorting all the posts requires a fair amount of server-side work on a busy site, so I can see why there might not be much of a push to implement it.