If I Smoke Marijuana I Can Become Like Michael Phelps, The Worlds Best Olympian?

His offense? He tested positive for marijuana. Now Williams, who just last month ran the fastest 60 meters in the world, will be ineligible to compete for the next three months and will have to complete an anti-doping educational program.
http://blog.mpp.org/prohibition/another-world-class-athlete-g...

So what gives here? Michael Phelps is known to use Marijuana and he says I am sorry, and is allowed to compete. Yet other people who have used it, are not.

I bet a lot of people who serve time in jail for using Marijuana could be home free, if they were allowed to use the Michael Phelps I am sorry plea.
http://www.telegraph.co.uk/sport/olympics/swimming/4425453/Mi...

http://www.howstuffworks.com/athletic-drug-test.htm

Mr. Phelps may not have been using Marijuana during the London Games, but the question remains, how is it he was allowed to participate, when others are/were not?

Marijuana can also be known as a Sport Enhancing Drug, since of course it has been used for the treatment of cancer.

My question is how can I think Michael Phelps deserves his medals, when clearly he violated the rules, and got away with it?