There's a difference between unique style, and unique function. It's possible to have a unique style while still taking advantage of existing affordances. The visual style has to work with the affordance for it to be useful, but they aren't in lock-step.

For example, both a button with a gradient simulating a curved surface with top-down lighting, and a button with flat color but a drop shadow indicate they are to be pressed. But, both can have a very different visual impact.

The same is true of knobs, switches, push bars, and so on. It's possible to vary the style without straying from the established affordances present. The article's point about Bootstrap is that people are given a factory for making different color doors and windows, but not bothering to change the colors despite the ease of doing so that the framework provides. The result being that the houses are all starting to look kind of dull.

> There's a difference between unique style, and unique function

just how many way can you click a button?

If the button requires click and drag, like the shutter button for Mattebox on the iPhone, then it's unique compared to the other ordinary shutter buttons, even though visually it's barely different. (Fortunately, it's different enough to indicate what needs to be done — affordance.) That's a fairly unique interaction, certainly within camera apps, that doesn't require much style differentiation.

Using the door handle metaphor, and example would be a handle that's a few inches from the floor and looks almost the same as a handle at 32 inches but is better served by pressing with your foot. Visually the same but very different interactions.