Mmm.. I don't have one of these, but my bet is that, if the edge was very clear and smooth, then it probably wouldn't work as well for giving that neon glow effect.

Having a "dirty edge" here probably helps with the necessary light diffusion, improving the overall effect when backlit.

We've got a very similar discussion somewhere about backlit buttons, where the clear and smooth leds and buttons are NOT what is needed to make them glow nicely!

Cheers