For example, I could probably build in 10 hours a customized, nice-looking Twitter bootstrap Rails site with Stripe integration and deploy it onto EC2 and set up Capistrano to integrate with whatever existing Github flow they have...but then when it comes to building the admin...um...developing the admin from a technical standpoint is non-trivial, but developing it in such a way that it is hassle free from the client...How exactly does the developer do that, without extensive consultation time with the client? And what if their in-house developer (let's pretend they have one who is competent) doesn't have a workflow like I imagine a good workflow should be?
In other words, I'm having a hard time imagining what a rockstar developer could singlehandedly create that would be spectacular and would be something that that mortals can use and maintain on their own...but obviously that's why I'm not a $200+/hr freelance developer.