A lot of sites insist on each downloader uploading in return to a ratio of between 0.7 and 1.0, sometimes more.
I agree in principal with what your advocating, but if I'm to be totally honest here, I can't imagine how you could police/monitor your proposal.
To give you a quick example:
I'm currently hosting the GWX2.1 torrent from a private/home server. This is not a file storage location such as FF, Megaupload or Rapidshare........a home server.
I am more than happy to post a screenshot if you wish but here are 3 1/2 months (torrent added 16/12/07) statistics:
382GB uploaded...Peers (those downloading) 11......Seeds (those who have it still on their hard drives and appear to be connectable online) 15.........MOST IMPORTANTLY, those Seeds currently online other than the server torrent host.....0
I've observed this pattern of behaviour since the torrent was announced
Now that's LEECHING