tl;dr: venti with compressed blocks, delivered as a new archive format because tar isn’t good enough anymore.
And there I was, wondering if I’d hate that too. Thanks for the tl;dr.
Pottering wouldn’t be able to sleep at night without reinventing something with added complexity. :P
joking aside, rsync isn’t a bad platform upon which to build by any means, but I’m a bit surprised it isn’t based more on a torrent-like protocol.