One thing that a parody can do that an original cannot is a marked deviation from what one expects to hear. This can serve to amplify the comic effect, or cause the intended message to strike home with greater force.

Walt Kelly could have had Pogo make some original comment about our tendency to be our own worst enemy, but I doubt very much that it would have had the staying power or the impact of his twist on the famoust Oliver Hazard Perry quotation, "We have met the enemy and they are US".