im sure if you sit down and talk with someone who is involved with the business he might tell you but of course everyone in public will deny it. i spend a lot of time on the various anabolic web forums on the internet and when you have some experience with the stuff you know they are gonna use. also a lot of the actors that get in shape for big roles you can count on the fact that they are using also.
I don't doubt that a sizable percentage of pro athletes are on steroids, but 90% seems high.