I'm going to go out on a limb and say most people don't really go through the math of it, and instead focus on the specter of scalability instead. It's temptin

I'm going to go out on a limb and say most people don't really go through the math of it, and instead focus on the specter of scalability instead. It's tempting to do when you're starting something new, and you think of how painful it is to switch hosts later; and the cloud has the suggestion that scaling is much easier -- "Just add more servers!" Basically, it's a premature optimization.