I think Chris nails it with this one on the head, but the whole article is really worth the read:
What websites are being asked to do is rising. Developers are being asked to build very complicated things very quickly and have them work very well and very fast.
The rate at which the complexity of our jobs is rising is astronomical. However, the final result — which still just a “website” to a layman/user — doesn't necessarily reflect that. People still think that when they are commissioning a website today, that it's the same type of work that it was five years ago, when in fact it is anything but.
To add to Chris' main question from the article, we often get asked “what it means being a front-end developer nowadays?”
I'm here for the TL;DR, man. Can you just tell me should designers code?
My answer is still the same, but I can now definitely add something to it. Yes, designers should code as in knowing how HTML, CSS, and JS work, and they need to be aware of how they affect performance in the browsers. They don't necessarily need to be able to build the interfaces they design themselves, as long as they are aware of the technologies being used.
This essentially means that designers should know how to code as if it were five years ago.