[Turbine]

If when you view the page you can visually see the shadow's start and stop points that means the shadow is not uniform enough to create a consistent effect. The idea of making a wide image with shadow effects on either side is perfectly fine, the only problem that will come up is making the image design so that the shadow appears completely uniform, which is quite easy to do.

Also, the site you linked to to show an example of what you didn't want, what is happening there is the designer of the page is using .png and is doing a shade gradient. The site that is mentioned for pulling off the design the way you want is using the typical vertical-repeat method. The Nintendo site's method is more advanced as they're using PNG's alpha channel, where as GIF is binary transparency, which means a pixel is either see-through or not, there is no percentage. PNGs are capable of semi-transparency, BUT it has always been considered a very crisp format, but what it comes down to is the shadow IS uniform, it is simply the way the background combined with the alpha-channel combined with the color overlay that makes it look like it has interrupts, so it's not the image not being uniform that is the problem, just so you know. Hope this helps!

-Turbine