I agree somewhat, but I think the protocol needed to come first. Can you honestly say that in its absence, multiple clients would be able to implement these behaviours in a uniform manner?
The fact that there's a concept of a "session" demarcated with LOGON/LOGOUT, sequence numbering, resend semantics, heartbeating - all this had to come from... somewhere.
Put another way: if you get 10 brokers developing their own REST/HTTP API's, what is the chance they'll normalise on a similar set of core concepts?