Surely you didn't mean to type "physical". Even if Amazon did nothing else, they'd still order, receive, unpack, assemble, rack, stack, power, cool, and network their servers with an economy of scale that I can't possibly match.
And who could ever claim that AWS requires no maintenance? It takes plenty; I should know. But the problem isn't that Amazon is necessarily less expensive, or more expensive, or more reliable, or less reliable. All of that depends on the context. The problem is that the context is rarely reported in this genre of blog post. These posts tend to fixate on the size of the hosting bill. This is the year 2013, and unless its business model is hopelessly flawed, the hosting bill is one of the smallest problems a new company will ever have.
But maybe I'm wrong about that, so I wish these writeups would provide more context to explain why I'm wrong in this or that particular case, and by how much. Yes, I see the hosting bill is down. But are the savings significant to the business? Did the migration take one engineer-day, or twelve, or thirty-eight? Did it reduce the size of the codebase or increase it, and which modules were affected? Is the time required for testing and reliable deployment up or down, and by how much? How has your planning for various disaster scenarios changed? Are you getting more or fewer alerts in the middle of the night?