Sure but hey, if you buy the version from Amazon, you're only getting 1/3rd of the product, too. I can't guarantee you get updates I push to the book, and you also don't get the epub and PDF formats.
But yes, I get more money because there's no Amazon middleman. Even if it was the same price on Amazon, I'd get less royalties.
I will always look for a book on amazon (as I know, from working for a publisher that amazon demand cheaper books). As a consumer why would I act any different?
If you push an update, I can buy that as well on amazon (and still only spend $14.40 total)...
EDIT:
1/3rd of the product? do you mean there is only 1/3rd of the book? or are you referring to the formats? That is an odd way to describe the product. I would say the product is your knowledge, not the paper/format it is produced in.
But yes, I get more money because there's no Amazon middleman. Even if it was the same price on Amazon, I'd get less royalties.
Just being honest.