@Brent cv,
They do control the amount of alcohol in certain states. I know that Oaktonarcher cannot purchase pure grain alcohol (190 proof) in his state, but I can here.
They wouldn't need to worry about limiting THC. You can't OD. It'd be like cigarettes. You have Camel Filters, Camel Lights, Camel Turkish Gold, Camel Turkish Silver, etc.
Oh, and btw I don't agree with 100% of that link, it does contain good info though.