I mean, they can, but I don't think they'll bother busting people in their homes. Ann Arbor is a good example (not quite the same, but almost decriminalized).
I think that if/when more states start to pass decrim laws and 'recreation' laws (see Colorado, Washington), the feds will have to choose between continuing an unnecessary, expensive war on drugs or changing
national laws to accept the more lenient state laws. It's not going to stay like this (legal per state law, illegal per national law) for very long, and legitimate businesses can't thrive under current laws.