"Car purchase" got votes because its author mumbled things about biases and rationality in it. The dieting and headache prevention got votes because the community recognises them as "rationality topics", topics which have been used as examples where majority wisdom is wrong and rationality can help. I suspect the Alicorn's post got more votes because people saw that it was written by Alicorn.

Physics is not a recognised rationality topic, and so the above post got voted down. Had it been about quantum physics it would have received upvotes.

N.B. I had downvoted all three of your examples as well as the above post. I also downvote all the AI articles.