It's also better for most video content; an iPad watching a 16:9 TV stream is only using 75% of the screen. Apple itself has moved to a widescreen format for the iPhone 5, and I wouldn't be surprised to see a future iPad do that too. I think there's lots of value to squarer aspect ratios for desktop/text usage (c.f. the Chromebook Pixel moving slightly in the opposite direction), but for a media device like a phone or tablet I'd expect them all to converge on the aspect used by content.

Obviously none of that has to do with the bad math in the MS ad. The iPad screen is, in fact, larger than the Asus one.