The mini's recent refresh made its base cost $699, actually.
Yes, and it is also a new type of product. Macs (and PCs) have been around for decades.
Are you saying it should have been easier or harder for Apple to move this many units?
I imagine steve19 is saying it should be easier to move iPads than Mac computers. People already have computers in the traditional sense and are generally happy with them; there isn't a pressing need to upgrade more than every few years. In contrast with this is the iPad, a brand new product that people can purchase on an impulse (due to its lower-than-a-computer price) and show off to friends.
They do cost a whole lot less, but I wonder how much the cost to make. In other words, what is the profit margin on each one?
Well the article said that Apple had a slightly smaller profit margin than that of previous years and they blamed that on the iPad. So it seems that the iPad profit margin is smaller than that of the Macs and iPhone.