One thing to remember is that athletes don't necessarily use what they would want to use, they use what they think they can get away with - which might theoretically provide a benefit.
It's not certain at all that all illicit drugs actually help.
What I'd like to know is what legal OTC and not-banned substances are in the athletes blood during the olympics. I bet there are a lot and that there are some trends and weirdness - eg Viagra and acetaminophen in a lot of samples.