Joel Spolsky says that some individuals appear to have been born without the part of the brain that understands pointers and recursion. Maybe that's the case here?
Maybe. It might just be that some people tune out when the rules are explained. Sci-fi geeks won't (because we know they are important). If you expected Inception to be an action flick, you might tune out during the techo-babble (since it's often just an excuse for blowing stuff up) and not be able to unravel it.
I haven't seen the movie, but reading this reminded me more of a state machine. It seems like it would be tough to keep track of 4 states at once and jump back and forth between them. (though it might be easier for engineers since we have been training these mental faculties more than most others)
Dunno about "without", but certainly not well used. Once explained recursion to someone using a simple programming example; we stepped thru it for two hours before he got it.