Are all the wave patterns hitting our ears the same for all types of speakers and rooms? If not, then isn't it possible we may interpret the sensory differently?
I don't think it is that difficult to create a sense of ambience behind us if the wave patterns hitting our ears from behind, top, and sides are significant enough - I mean with all the waves bouncing everywhere.
Remember that dipole/bipolar speakers have drivers in front and in the
rear of the speakers and their polar responses are quite different. Their wave patterns are more diffused and a lot less focused than front radiating speakers.
Having said all that as a debate
, I do prefer movies in 5.1 over 2.1 every time when the movies are encoded for discrete 5.1.
My only point is, some DTS discrete 5.1 movie soundtracks still sound fantastic in 2.1. This may not be enough for most of us. But it may be enough for some guys.