tl;dr: This is an evolution of browser standards, not a revolution in consumer software (from an average end-user POV)
From a developer POV, this is pretty cool because now it is (or at least, is well on its way to being) significantly easier to build an app that relies on real-time media shared between peers with only the only onus on the end-user being having an up-to-date browser. The simplest and most obviously useful application of this is a basic VoIP tool.
Also, why is this stuff better than SIP related technology from a while back?
The excitement here is that this is a non-flash solution, so technically it will work on any device that can run Chrome, regardless of whether or not it can / wants to run Flash. So in the near future this may make it into Chrome for Android and iOS.
WebRTC is a very necessary step in removing Flash's hooks into the modern internet; after this, there will be very few reasons to support it at all anymore. And that is a very good thing for speed, compatibility, and security.
Neither of these automatically grants any additional security. If anything, it is just tying us to fewer vendors that can do this. I guess it doesn't matter, but I can recall a time when I was able to choose which application handled certain content type. We seem to be saying we do not want that for video now.
I guess I can see how it does. I mean, the idea is that this protocol can be used to communicate between two vendors. But, that can already be done. It is done, on a regular basis. What, exactly, makes this special?