Except that in the Monty Hall problem something has changed after the initial choice: one of the previous options is proven to be a goat. No such change occurs with the two envelopes, no new information is made available, thus no basis for switching.
There is additional information in the Monty Hall problem: the host never opens the door with a car. In the two envelope's problem, the "host" merely restates the question no matter which envelope was chosen.
Folks, it's an analogy. An analogy compares two different things... trust me, I know they're different and I know in which ways.
All I was saying is common sense doesn't get you far in the Monty Hall problem. It really doesn't:
>[Vos Savant] received thousands of letters from her readers; 92% of the general public, 65% of universities, and many with PhDs, were against her answer.
Thus, it's kind of silly to say we're wasting time by going past a common sense analysis of something. It's also revisionist to say common sense does help you solve Monty Hall.