"In A/B tests, we tried delaying the page in increments of 100 milliseconds and found that even very small delays would result in substantial and costly drops in revenue."
Seriously though, site responsiveness is important. If you haven't seen it YSlow is pretty awesome (http://developer.yahoo.com/performance/).
In either formulation, it's within the range of plausibility.
In my experience, a single change that makes a web server faster causes a slow, steady increase in traffic over the next few days/weeks, as the audience reacts to the new responsiveness.
Note also that Google considers page load latency in scoring ad relevance, and almost certainly natural search result ranking as well. So everything improves with speed.
Just to be pedantic an eye blink takes 300 to 400 ms. Amazon's claim is that delays 3 to 4 times less than an eye blink are annoying to people.
Mean reaction time for a human is around 200 ms for a visual stimulus so Amazon is talking about faster than normal reaction time as well.
Frame rate in video games is between 30 and 60 frames per second or one frame every 16 to 33 ms. Cinema is 24 fps or one frame every 40 ms.
So it would appear that Amazon is saying that a delay that a human can perceive is troubling and results in lost sales.
Are these techniques patented? Otherwise how does one "hoard" a technique?