Well, after Falko published his rdiff backup tutorial I wanted to use that. However my friend is using Suse 9.x and I have Debian 3.1. The native packages that are available through yast2 / apt weren't compatible and I didn't want to invest too much time into it.
Soon after Falko published the same guide for rSync and I found Mike Rubels site where he shows how to operate with hard-links to create incremental backups. So I tried rsync for backing up and the Suse and debian one were compatible with each other. That is my reason for using rSync
I think also the algorithm of comparing files and then transferring them are different but I didn't put too much into research of that.
Well, that isn't exactely an answer to your question but my motivation why I chose rsync