It might not always hold true but with the way the web is now, I don’t know how you can really design a website successfully without at least the basic knowledge to code the html and css yourself. An architect who doesn’t understand basic building principals isn’t going to get very far. The same hold true for a designer who cannot code. Static sites are going the way of the dinosaur and if the designer doesn’t understand how content can grow and expand they will not be very successful creating the UI.