Also, you better trust Amazon to fairly determine when to scale up... more instances == more profit for them.
Trust of a web host is of paramount importance. I know a lot of people who stuck with more expensive hosts just because they trust them and have a good working relationship with them.
re: trusting Amazon to scale, as they say in the release notes, they provide a detailed audit of scaling activity. After all the work Amazon has done to help their customers, I doubt they're interested in grabbing a little cash from inappropriate scaling.