This was a problem for me even before Last Crusade. Indy shows great skepticism of the supernatural in Raiders, but Temple shows us that he's already experienced wild paranormal phenomena prior to the events of the first film. I've never really understood why Temple was made a prequel. Just...
Carlo's comment reminded me--although I had major issues with the "fridge" scene itself, I absolutely loved the following shot with Indy and the mushroom cloud. It's one of my favorite moments from the whole series, and definitely my favorite part of Crystal Skull.
Actually, when watching Iron Man, the first thing I thought of when that scene came up was the "fridge" scene from Indiana Jones. I don't think it's nearly as bad as the fridge scene, but it did stand out as wildly implausible in an otherwise great movie. Of course, I also enjoyed Indiana Jones...
What definition of "plausible" are you using that includes a refrigerator being hurled through the air intact instead of obliterated on the spot like every other object in the vicinity, and a 50-odd-year-old man surviving being thrown miles through the air with nary a scratch, simply walking...