For Amazon, getting a 0.1% increase in revenue from changing the color of a button would be a big deal. If Amazon paid $50k just for that one color change they would still be millions of dollars ahead.
For a smaller business a 0.1% change would not be as significant.
For Amazon, A/B testing a button color could have a huge effect.
However, being "prettier" might not do a damn thing. Heck, it might HURT them.
The author, I think, is talking about graphic design. His point would obviously fall REALLY flat if he was talking about UX design.
So, what is UX?
If you have 5x less traction than a competitor but you can monetize yours 10x better, you're in a way better position. Aesthetic design can be a huge driver in higher value users.