The argument is that the two should be able to transparently interop together, and specifically that RFC 723[0-5] simply codifies the way HTTP/1.1 already works in the real world.
Shouldn't minor revisions of HTTP interop anyways? I.e. a HTTP/1.2 server should be able to talk with a HTTP/1.1 client even if they use different minor versions in their protocol string? So, it "SHOULDN'T" hurt to bump the version to 1.2, plus it would make it easier to identify up to date spec compliance?
We'll see how well that goes.