Dunno, have you tried asking the authors of those programs why there is no Linux/Unix version? Not much we can do in way of answering your question since, AFAIK, the authors are not on this list.
Utorrent and BitComent are written by C for Window$, while Utorrent can run on FreeBSD and Linux through wine or cedega. So I think it should be very easy to port to Unix/Linux. The good news is the developers of Utorrent said a Unix/Linux version is in their plan, but the bad news is we haven't seen Unix/Linux version yet.