HTML5 WebSockets are new to the block and there are several key browsers that do not support the protocol. Until the users of those browsers can upgrade to newer applications, developers would benefit from abstracting this protocol from the StreamLayer.
Ideally a two-way messaging provider basetype would allow for implementing third party or custom implermentations such as Socket.Io or SignalR. Stream Layer can better integrate with current infrastructure and provide more options to support browsers that re not ws:// enabled.