I think 2x is a bit optimistic, if you just compare what kind of hardware you get by renting a dedicated server compared to EC2 it can easily be 5x or more. Of course that compares very different things, and doesn't mean that renting dedicated servers is always cheaper. The comparison gets much, much worse when significant amounts of traffic is involved. And scaling down isn't so much more difficult than with AWS within certain limits.

Comparing managed services like databases is maybe more meaningful than just EC2, but also so much more difficult.