On a tablet, bigger doesn't equal better, and a very common sentiment is that the Mini is the ideal size, with the iPad full-sized being unwieldy for many uses (any situation where you hold it in your hand). So I'm not ignoring screen size, but quite contrary am saying that smaller, in this case, for many purposes == better. Obviously that is to a point, but for common uses the iPad Mini is very close to perfect.
To put it another way, now that Apple has equalized the hardware (same resolution, processor, accouterments), they could legitimately pitch the Mini as the more expensive, premium device (fitting more capabilities in a smaller space). Of course they couldn't only because they originally intro'd the mini as the discount device, but had they not it would be a legitimate angle.