That was an arbitrary number, but I don't think that is true. It doesn't take much functionality before you will start needing the power of a server in the $500 range. Many apps today do a lot more than serve up static requests. I run a php server with just a few thousand daily active users and we need a $250/mo server.

You have your app, and database, and then your logging, tracing, and tracking stack and It all starts adding up pretty quickly.