Ah, okay now I get the subtlety, I stand corrected.
I'd still argue that there are times that you do have to use completely custom controls, like the case with the date-pickers. Not only because you cannot style them, but they also have a lot of API constraints, and accessibility problems. Even the example in the article, the beloved text area, has a lot of constraints like it's quite cumbersome to get the selection coordinates and it's impossible to offer any highlighting, so welcome to the world of contenteditable!
I completely agree that we should try to compose the native UI controls instead of reinventing the wheel when possible (like the text-input for that date-picker modal).