[toolate]

Amazon's API format is irrelevant because their service is so popular. Once the API is stable and client libraries are available for common languages most developers will be unaware of the actual mechanics.

If you're launching a startup then you don't want to give your early adopters an excuse to not work with your API. If you're developing an API for internal use then you won't be using an off the shelf client library in any case.

Furthermore, a clean API is a sign to other developers that you know what you are doing. If you are targetting an industry where coders get a say on whether or not they will choose your service then you'd better put your best foot forward. I've seen far too many APIs that show a company has no clue on the technical side, which causes me to cast doubt on other parts of their service.