Just to add to what I said. I found a good interview with Lance Barr (the designer of the North American NES and SNES casing), and this is what he said:
ND: The Super NES design is quite square compared to the Super Famicom. What was your motivation for going in that design direction?
LB: The Super Famicom was maybe okay for the market in Japan. For the US, I felt that it was too soft and had no edge. We were always looking at future modular components (even the NES had a connector on the bottom), so you had to design with the idea of stacking on top of other components. I though the Super Famicom didn't look good when stacked and even by itself, had a kind of "bag of bread" look.
ND: Why is it that all the case designs have been handled by NCL from 1995 on? Do you have any input into those designs at this point, in order to ensure American appeal?
LB: Individually designing a product for a given market would definitely appeal to more consumers, and would be seen as having a more current, in style look. Because of the low cost of packaging, companies almost always individually design for each market--regardless of the language requirements since they know that for the cost, you can better reach your intended audience. But with products, the realities of manufacturing and time to market make it necessary to design in a single, world-wide style. Nintendo started to do this beginning with Nintendo 64. Of course the down side of this is that a given design never quite fits the needs of a particular market as well as it could had it been specifically designed for that market. Within these bounds, Nintendo localizes the hardware for each market, mainly thorough variations in color
http://www.nintendojo.com/archives/interviews/view_item.php?1130801472