I recall someone claiming to be an amazon developer one of the previous times when this happened claiming that they don't actually lose that much money. (sorry no link, my google-fu has failed me). A small number of orders where people are desperate are lost, but the vast majority of people generally just wait it out and make their order tomorrow instead.
10 years ago we calculated downtime at $100k/minute for the homepage. So when you tried to do an ajaxy thing on the home page and messed it up, even after testing, you had to write an email that calculated how much theoretical money was lost.
And sure, there's some elasticity, but an approximation is handy.