Perhaps, but hardly true of the movies quoted - for example Star Wars is one of the most obsessively detailed settings ever and is all the duller for it. We know exactly who Indiana Jones is (OK, elaborated over a lengthy story arc) and so on.
Big Trouble in Little China is an old favourite of mine, though, and it is laden with ambiguity. In fact, Kurt Russell's character is an everyman wanderer type.
-If it isn't true for movies, then why do you say that SW is dull because it isn't ambiguous?-SW's ambiguity lies(lied) in the background story
-Ij (Ijc, Iij, what?) mentioned specifically Temple of Doom, so it's a safe bet he didn't mean Jones' persona