I'm less surprised if AWS internally pays AWS list prices, because that's just internal accounting. From the even relatively small AWS customers I know, none of them needed to get very far into the 6 digits per year spend before a couple of quiet mentions to their account manager that they were reviewing other options was enough to get steep discounts.

Add in lots of credits, and if you pay list price, you're being taken to the cleaners..

I've done contract work for clients to be ready to migrate both as part of maximising credits and as part of negotiating posture, and the savings can be enormous (though it'd still usually be cheaper to use managed servers).