That's a bit of a misconception. From what I understand, Amazon's non-AWS branches don't get deeply-discounted services from AWS. There is a discount, but it's not enough to turn dark skies into sunshine and rainbows.
Amazon tends to want every part of itself to be in ship-shape, and giving itself a massive discount would discourage efficiency in non-AWS parts of the business.
Disclosure: neither a current nor former Amazon employee.
This is a misconception. Amazon wants to depict itself as wanting every part to be in ship-shape, but it does not operate that way and AWS is treated like any internal resource like printers and staplers.
AWS basically finances the rest of Amazon. It's 70% of its revenue (that is public info). Except for retail, the rest is all losses. So the discounts don't matter much, other branches just try to save money (frugality is one of Amazon's core values) but basically get what they need.
Amazon tends to want every part of itself to be in ship-shape, and giving itself a massive discount would discourage efficiency in non-AWS parts of the business.
Disclosure: neither a current nor former Amazon employee.