I see no reason why Apple has to stick to a Pro/Consumer industrial design scheme. It does not matter. During the color days, all of their products were colorful, except for the black PowerBook.
Just because some people here think it's cute and convenient, maybe even logical and easy to differentiate products based on design...does not mean that it works. Who the hell knows, other than Mac fans, that Apple does this?
The iPod is the perfect example of where Apple has contradicted this supposed law of differentiation. Metal/Plastic, wtf mate?