I think it's important to note as those sockets are NOT standard. Albeit with Nacl and the chrome store it seems that what Google wants, is that users do everything via their extensions, and via their store (bypassing the standard web while thinking they're on it)
Firefox has had sockets for a while and has also chosen to make them available to extensions only. Even Java Applets back in the day supported sockets only if you jumped through a bunch of hoops (if I recall correctly. it's possible you could only do socket communication with JNLP or something).
As far as I know, NACL is extension/app only as a way of controlling risk to the client.
Depends on what you mean by "jumped through hoops". You could open up a socket to communicate with the host the applet came from (lots of fun defining what that meant ;-) without being signed. If you were signed... all best might be off.
Some people have complained that Chrome apps "are just web links". This is a way for the Chrome team to show that Chrome apps can do something more advanced than what HTML5 allows today.
The functionality can be exposed on any webpage. It's likely that Google is only allowing it via the Web App Store for further vulnerability testing and moderation ability over the Web Store Content.
about:flags and two clicks will enable NaCl TCP/UDP sockets and a third click will enable NaCl on any webpage with a prudent and applicable warning about the potential security risk.
