Well observed. The problem with client to server RPC is that it's difficult to scale horizontally. When using pub/sub, on the other hand, you are giving control to your data consumers (frontend clients) so you don't run into issues of having to get references to specific users from your server (what if that user is connected to a different process/machine and not the current process?). I did a presentation a few weeks ago at my local JS meetup group which explained the issue better: http://slides.com/grosjona/realtime#/