With regard to your point on exposition on and the question "says who?"
Well David Mamet for one:
Any time two characters are talking about a third, the scene is a crock of shit.
Any time any character is saying to another "as you know", that is, telling another character what you, the writer, need the audience to know, the scene is a crock of shit.
http://ezinearticles.com/?David-Mamets-Rules-For-Writers---W...
Not having seen inception, I can't judge if the exposition somehow avoids this problem, but in general I feel like Mamet is as good an authority as any to appeal to :)