[TeMPOraL]

Different kind of patterns. Design is about visual abstractions; code is more about textual and conceptual abstractions. The design space of a visual medium tends to be much easier to explore... visually.

(Also consider that a typical way of developing a website or application UI involves everything from drawing on paper through painting in Photoshop through building mockups in a graphics-oriented design package.)

[chs9000]

I think at times we get too caught up in the visual components. Visuals like sketches and mockups and even code-less prototypes are perhaps best for communicating concepts, which is a part of design. But there's also the part of design that's less about communicating designs and more about applying the concept and designing a way that it can be created and engineered. That's where designing with code is extremely helpful.

So yeah, if I'm exploring or communicating ideas to non-technical people then yeah maybe code is less appropriate, but to say that you shouldn't design with code is ignoring a huge part of the design process.