Besides being early days as Ulf said, I think it is also because WebSocket itself is quite low level API. For majority of developers, it is preferable to work with higher level of abstraction. I think once there are more high level abstraction libraries or frameworks available using WebSocket as transport, we'll see more adoption and talk about it.
For illustration, most example on the web for WebSocket are dumb echo or chat server which is fine for show casing WebSocket itself. But when you want to start developing real application, a natural example where WebSocket will be usefule are online game or auction apps, you start have to think application context, how to group set of WebSocket connections that ties to particular interest (auction item), etc. You basically have to define your own higher level protocol for these, which is daunting stuff for majority of developer.
We don't see any typical Java developer write Web based application using java.net.DatagramSocket. Most of Java web developer is using Spring MVC, Struts, JSF which is higher level abstraction over Servlet API which is higher level abstraction over HTTP which is higher level abstraction over TCP/IP. In Web Apps world, WebSocket is pretty much at the same level as TCP/IP of networking world. It will probably another year or two before useful high level libraries/frameworks available for public consumption which will make WebSocket widely use.