In my experience, the "it just takes" path of development will lead to a user experience that breaks down fairly quickly in many content management systems.

The overall layout of a page becomes hidden behind layers of indirection in the CMS (e.g. you edit the hero here, and then go there to select it for the homepage, but the content for blocks on the next row of the homepage are maintained somewhere else entirely).

As an agency, it's not that strange to offer 'marketing services' which includes doing the content and layout for key pages of the client's website (like author's example of the iPhone 5 section on apple.com). It can be more cost effective to have a front-end developer update these pages if and when they change, compared to developing a complex CMS to handle constantly evolving page layouts.