[tzs]

> The only thing you get with FREE shipping is a receipt that doesn't include shipping as a line item

In practice, though, it does appear to be more than that. The vast majority of the time, the difference between the total cost if I buy from someplace without free shipping, and the total cost if I buy from Amazon with free shipping, is very close to the amount on the "shipping" line item at the first place.

It is just an illusion, as you say, but they made the illusion so good that I cannot usually tell the difference from reality when I'm comparison shopping for something.