Technically it is zero sum, but bittorrent prioritizes peering based on how fast your internet connection is. So somebody on dial-up internet probably isn't goi

Technically it is zero sum, but bittorrent prioritizes peering based on how fast your internet connection is. So somebody on dial-up internet probably isn't going to upload to anyone, while someone who has high speed internet is going to upload to many people. So somebody with high speed internet access might upload twice as much data as they downloaded. And while I don't think ISPs really care about you maxing out a phone line, they will notice you maxing out a broadband line. And bittorent will do that.