"Shipments refer to sell-in. Numbers are rounded. The definition of tablet does not include e-book readers."

So, in theory, the Kindle Fire is not included.
But, "sell in" and "bought by consumers" are not the same thing.

Question: If you (HTC, for example) were going to introduce a tablet and sell it worldwide--what is the mininum number you would have to make just to adequately stock the channel?

Shipment does not equal sales all you have to do is go into any store and see how many Android tablets they have gathering dust to realize sales are no where close. Only the Fire has had any real success.