Inexperience, yes. Caution? Not so sure. What comes across as caution seems more an indication of the man's lack of substance. He can only talk in platitudes and generalities because his knowledge of issues is so shallow. He's a creation of his handlers, a camel fashioned by committee to resemble what they think a statesman looks like.
I don’t know, he seems to have substance in the way Jesse Jackson has substance—other people’s stories he can tell, with a tear in his eye and a catch in his throat. Don’t discount that—it counts as substance in the post “I feel your pain” era.