> what protocols can be blocked but not shaped?
encrypted bittorrent and Warez for sure. But it's more complicated, read below.
> if you can block then why cant you shape it?
because it's not possible to recognize ALL p2p traffic packets. It's that simple.
Many protocols are recognized to extent they can be blocked only (not traffic shaped) as this was technically sufficient for bandwidth management purposes (=allow p2p during night, disable throughout day) and main reason is that it's not technically possible to recognize all packets. Nobody has the knowledge, time, passion, luck etc to analyze p2p communication to maximum detail... read something about it on ipp2p.org and other l7 filtering solutions. And yet, we're not taking into account ciphering here
Our biggest bandwidth hogger is dc++ then followed by bitorrent. DC++ is one of the oldest protocols, it's pretty straight forward and SIMPLE - yet we were not able to move DC++ traffic to another gateway no matter how we tried. And believe me, we spent a lot of time with this as it's causing us some technical problems and we are not networking novices.
Knowing some technical details about p2p protocols (search for technical p2p protocol description, there are several guides on internet), we simply won't devote our time to this anymore. You haven't seen a single person here on forum to report "I got it working, p2p goes to second gateway". And you won't see one soon.