The difference is, because of its prohibition, marijuana has a thriving black market. They need to stamp out the black market before they can get taxation to that level.
A friend of mine visited me in Denver from another state. He came back from a weed store with a little bottle and exclaimed "dude, this was only 10 bucks! It'd cost me like $50 back home!"
I'm really looking forward to seeing data on what happens to the black market for other drugs, with marijuana now easier to get legally than illegally.
