Where did you get the idea that the feds have surrendered when it comes to marijuana? Last I heard they were still arresting people in California and prosecuting them... Has there been a change in that I missed?
Yes. The rape of the Constitution known as Raich was vigorously pursued by the Bush administration, first being known as Ashcroft v. Raich and then Gonzales v. Raich. SCOTUS found that their level of government may do whatever the hell they want to and state laws be damned, surprise, surprise.
Now Obama's DOJ has adjusted course slightly, declaring that pursuing cases in states where it's been legalized isn't "the best use of resources". See, Obama can even screw this up. No change in the law, just a change in emphasis. US Attorneys can still pursue them if they want to, and I don't think "But your boss said this isn't the best use of resources" exactly amounts to a strong affirmative defense.