My experience, as someone who went from drinking 2-4 cups of normal coffee plus several black teas per day to drinking 1-2 cups of decaf (and no tea) is that it IS addictive.
hoc_age's answer that there are psychoactive chemicals in coffee other than caffeine makes sense to me. The decaf I drink is the Swiss method of decaf which is supposed to remove more caffeine than other methods.
Yet if I don't have my decaf in the morning I crave it - with the exact same feeling as when I would "need" my normal caffeinated morning coffee.
I've tried drinking Caro and other similarly flavoured hot drinks but my body still wants coffee, decaf or not.
It definitely feels like there is something other than caffeine that makes it addictive.
This is not withstanding that caffeine itself is addictive; there is much science behind that to be in no doubt. I had the worst withdrawal symptoms when I quit normal coffee that no amount of decaf helped with. I felt physically sick and had crushing headaches that lasted a week and got worse every day until they finally disappeared.