Well, from what I've been told, even just not pleasing someone, having studied in an "enemy" school, having a better level, etc. can be quite handicaping.
Some persons are just very influential. And I can only guess how Schiff's influence is like. And on the top of Schiff, there's the whole room looking at you, and you might well get a "bad" reputation for doing somethingof this kind.
Althrough I've not experienced it (in the bad way), I think this is really how it works. Peer pressure, reputation, relations, power, etc. are all things that can influence your studies and your carreer. And I bet a lot of students are willing to play the game - by lack of courage or by what they think of as intelligence, or both.
Just being seen in a masterclass might be worth it for them.

I personally just wouldn't attend a masterclass with a sh*tty teacher even if he's a world-class musician (:

Salut l'Andorran !

You don't think Andras Schiff reads the internet? I know some of these artists live in another world altogether from everyone else, which might very well be necessary for them to concentrate on their art. Still, artists have to be mindful of what the public thinks of them, and the internet is a great tool for finding out what a select and informed section of the audience believes. The Forum is probably one of the better such sources, so why wouldn't Mr. Schiff be aware of and ready for someone who shows up at his master class to play the first movement of the Hammerklavier sonata?

The burning question is: will it change his attitude towards his victims (a.k.a. 'students')?