Bittorrent as a general transport service?

Why is it that every AnyAggregator brings it’s own Bittorrent with it?! DTV and [iPodder][2] even bring their own Python down to my disk… Why don’t we have a general transport mechanism that different Applications may use? Like a system wide or lan wide bittorrent service for file sharing and a local jabber service for instant messaging and presence. So any application that i.e. aggregates video clips or mp3 via rss and uses bittorrent to download this files may use the bittorrent service that is provided by the desktop, if the download has finished the application may notify the use using jabber and drop him a like to the file.