From what i read on Ars, [0] IE seems to have something else called CU-RTC-Web a competitor that doesn't require SDP like webRTC does, an IE to chrome demoing it was given recently [1], from what Ars said it may be that WebRTC could run on CU-RTC-Web, hopefully that or we have two "standards"
[0] http://arstechnica.com/information-technology/2013/01/micros...
[1] http://blogs.msdn.com/b/interoperability/archive/2013/01/17/...