I think the reason it works on Big Thunder and not on Space or Mulholland is that on Big Thunder you have a point of reference. Like it or not without a steady point of reference you will not continue to look at the same thing at all times, thus not creating the "Goat Trick" on other rides.
But since on Big Thunder you have a point of reference, keeping your eyes focused and your head pointed at the goat while the train whips around it you therefore feel it more.
And yeah ... I'm joining the group. I love busting myths.