It's also MUCH easier to setup/run in a multi-layered stack (e.g. Pound/HAProxy > Varnish > App Server).
As per usual, WebSockets is what the "cool kids" use, even when it's often much less appropriate and much less flexible.
The key thing is that a proxy/load balancer doesn't need special cases to support EventSource like it needs (and often doesn't have) with websockets.
