The cyclical “should designers code” debate wears me out, but Stephen Hay’s post is a great read in and of itself. I like that he gravitates towards the value of prototyping:
As designers for the web,[…] you are researching, structuring, adapting, testing, laying out, wireframing, setting type for, composing, and [fill in the blank]ing something that people will read, interact with, love, hate, tell others about, and perhaps take with them everywhere they go. And the medium is right in front of you, every day, so you as a designer for this medium have the opportunity to use it to prototype what you’re designing.
Prototyping is about asking reality for feedback.