Yes... it's psychological addiction. I was responding to someone who clearly thought MJ was a 'junkie'. They were implying that MJ was addicted to substances he was taking himself, as in 1993. The difference in 2009 is that the drug that killed him, he was receiving in one nightly intravenous dose rather than because he was popping pills to get his kicks.
I might have a psychological feeling of dependency for Weetabix, thinking that i can't function during the day without eating them in the morning, but that doesn't make me a cereal addict or even a junkie.
You can be addicted to caffeine and also the psychological aspect of addiction is important - I'm probably a recovering caffeine addict - cocaine is not very physically addictive but is incredibly psychologically addictive for example.