Hardly, Tim. Look at this example that the Wikipedia article uses:



The tablet's screen dimensions fall outside the yellow box, since we have 1.66:1 ratio, as opposed to the 1.56:1 of the yellow box. I have found that there is very little (of importance) lost by cropping the edges.

Having said that, I'm not advocating cropping as a universal rule. I'm just saying that for most mobile use-cases, the pleasure of full-screen video outweighs the lost picture on the edges. We're not talking Imax here, we're talking about a handheld device.

And I must remind you that the more unused, black screen you have above and below your video, the more lost information you have within the picture. When you're talking about a small screen like the tablet's, it is a great loss indeed. All sorts of little details get lost because the picture is so small, just because you want to see what's going on in the far edges of the picture.