Good point, but that's a recent development that's contrary to trend. Looks at all of the federal-state disputes and you'll see the overall pattern.
Interestingly, this compliance is enforced by federal matching grants. In the 1980s, the Reagan Administration got the states to jack up the drinking age to 21 nationwide by threatening to withhold highway-fund matching grants to states who didn't have 21 as the minimum age.
Those states that legalized marijuana did so without the Obama Administration putting up a fight. Question worth pondering: will the Trump Adminstration fight it? From what I read, Trump's DHS pick is a hard-line Drug Warrior.
Trump will not touch weed, since it would cause a Political nightmare for Rep. in 4 years. Over 75% of the country is now for it (at least medical) Republicans are for States rights. If Sessions was President I would be worried however, I high doubt Trump would approve any crack down on Medical Marijuana. I expect them to actually legalize Medical fully in Jan. Trump is on record recently saying Medical is a States rights issue. Its hard to say what happens to Rec. weed. Mostly likely they would want to regulate heavily and tax it!
You could be right - to be quite frank, I hope you're right!