Github is to coders what an online portfolio/web presence is for designers. Look at the design industry... corporate designers and grads and freelancers used to all have a hard copy, artfully crafted portfolio on sensual-to-touch paper stock.

That's gone. And no one cared if the corporate designers didn't have time to create a website. Even if you still have an amazing portfolio (which is the resume for the designer), you better have something online (whether they are personal projects done outside of work, or glimpses of projects done at work).

The paper resume is going away anyway. And then when HR finally gets up with the times, do you really think they are going to say, "Aww, it's ok, we understand you didn't get on Github because you were waiting for us..." No.

HR people hiring designers using their online portfolio is a lagging indicator. And the same will go for HR people hiring developers based on Github.