Here's my personal opinion that I believe is fact. First off, I seriously doubt that the "top riders /best riders" could really careless if they ride bicycles with disc brakes. When you are a professional, you have a job to do and you need to do it. Pros do not make excuses, they make results, it is always the next to best who make excuses why they are not best. Like Ricky Bobby says: 2nd place is 1st place Loser.
Secondly, I think this conspiracy is greatly fueled by all the want to be pros who just spent +$15,000.00 dollars within the last couple years on their prize possession with rim brakes just to find out it is now obsolete. ouch!