It's not just that Amazon has done the math, it's that sufficiently liquid cryptocurrencies will, by the efficient market hypothesis, quickly gain enough value to make mining on whatever Amazon offers no longer profitable. As soon as you're able to profitably mine without an up-front capital investment, people will take advantage of the arbitrage opportunity until the market adjusts its price, and if the currency is designed at least somewhat competently and has enough of a working market (both of which are definitely true of Bitcoin), that won't take very long.
Cryptocurrencies are the invisible robot hand of the market. (Which is, I think, not a claim about whether they're good, but certainly a claim about whether they are to be feared. If you squint hard enough, the giant Bitcoin mines in China are the work of an unfriendly AI employing people to make paperclips.)
Cryptocurrencies are the invisible robot hand of the market. (Which is, I think, not a claim about whether they're good, but certainly a claim about whether they are to be feared. If you squint hard enough, the giant Bitcoin mines in China are the work of an unfriendly AI employing people to make paperclips.)