The last few years I commuted on a bike with 20" (451mm rims) tires and I agree with vol's last post that the tire life was definitely shorter - both because of more revolutions for a given distance but also because the shape of the contact patch is shorter and wider resulting in a bit more wear of the rubber tread per revolution.

But I disagree with the last point in the OP - my riding position is just as high on my bike with the 20" (451mm) wheels as it is on my 700c (622mm) bikes.