I must not be the only one - I'm rsyncing .tar.gz files and notice that every time the full file gets rsynced rather than the differences. Reading into it it seems back in 1999 someone created an algorithm that fixed the issue http://svana.org/kleptog/rgzip.html (only 5% of data needed transferred)
Has this gone anywhere since, how do I create rsync friendly .tar.gz files?