Monty Hall revisited, with a twist- survey

[Easy E]

Don't want to bring this up again, but in the Sunday Parade magazine, someone wrote in about the Monty Hall/intuition "puzzle".
He THEN said that one of his students posed this variation:
Suppose I am taking a multiple-choice test. On one question, I randomly choose 1 of 3 answers. Then the instructor says that one of the remaining two choices is incorrect. Should I switch my choice?

The "world's smartest woman" (or is that human? I forget what Marilyn vos Savant claims) said that the answer was: it doesn't matter.
She did NOT, however, explain her reasoning.

What am I missing here, because it seems like the exact same thing? Does it have to do with the way tests are scored, or that one wrong/right answer won't make a difference?


Monty Hall Test




Extra credit for detailed answers.