Per user limits are not easy to implement, maybe easier to visualize - consider that there are a bunch of packet gateways sitting behind a load balancer and each HTTP session may end up on a different server. There is no entity that counts the live bandwidth usage on a per user basis, let alone control it. Billing and metering is done on a session basis through logs. So from T-Mo's point of view it is much easier to detect a HTTP session as video and just throttle that session.