When LW user Joe shares a popular file, tons of uploaders will flood his upload slots. This is not desireable for Joe because he is on a DSL connection and he gets penalized whenever he uploads too much.

It's also bad to the network for several reasons:

1) When Joe's upload slots are maxed out, each downloader's download speed will go down.

2) People who want to access Joe's less popular files won't have a chance because Joe's queued up with requests for the more popular file. In general, this translates to less accessible files on the network.

3) A possible result might be that Joe will be more reluctant to share files that are high in demand. (= less files on the network.)

If LW did torrent-styled uploading of popular files, then I envision uploading would work something like this:

User1 asks for Joe's popular file. Joe's LW allows the upload to begin because User1 is the first person to ask. Then comes along User2, asking for the same file. Joe's LW sez: "Gee, sorry, my hands are tied. go ask User1 for a partial download." Then User2's LW sez: "OK! I'll go download from User1." If User1 isn't cooperative with uploading Joe can cut down his download rate and divert traffic to a more cooperative user.

Well, more on better uploading can be gleaned from <a href="http://bitconjurer.org/BitTorrent/">bittorent's</a> website, I suppose.