Think of WebRTC 1.1 as a slightly lower-level API with more controls for the same components that exist in WebRTC 1.0. For advanced applications, this additional control is very important. For basic applications, the differences in the APIs aren't as significant. One is not more secure than the other.

The WebRTC 1.0 API can be implemented on top of WebRTC 1.1. The wire-level protocols are the same, and so a WebRTC 1.1 client should be able to connect to a WebRTC 1.0 client (modulo all the normal interop issues that exist regardless of the API version). It's just a matter of which API the JS sees. It may be that by the time IE implements WebRTC 1.1, there will be JS libraries that implement 1.0 on top of 1.1, so that you could continue using the 1.0 API if you want, even in IE.