I find it hard to believe that they'd knock somebody out because of repertoire choice, they just shouldn't have let them enter.
It is the quality of playing that matters, they just want you to play certain things well. I don't agree with it, but I can see the logic behind stipulating a choice of composers that are acceptable.
I like these pieces that I mentioned; to a large degree they are my free choice. I could have played a bunch of different things, but here is the "logic" behind my choices and the order they're in.
I begin with a simple, sweet Bach prelude, and go into a fugue that is more complex and interesting, with an enjoyable melody. If done well, they would be a primer of sorts, and would interest the judges. Then, the Beethoven has a good deal of energy, as well as some nice lyrical sections; for balance. After the powerful ending, the Rach has a soft and sweet opening, which devlops into one of the most powerful climaxes I know of in solo piano repertoire. There are some beautiful melodies in it as well.
I do see your point, though. It is being rather cretinous to stipulate that I can only play 1 movement from a Sonata.