I think what that post is trying to say is this: focus on your core competency. Amazon is good at cloud computing, Netflix is good at renting/streaming movies.

However, there are some cases where "core competency" is a vague term. Take Facebook for example - could they outsource their infrastructure to somebody else? Given how much data they have to handle, probably not. When you get to the point where scaling requires very low-level (Hunch) or massive (Google or Facebook) optimizations/deployments, you might be entering the business of handling intricate infrastructure yourself.