Resumes are for deciding who you're going to interview. If github is the new resume, then you're not going to know about the side projects.
I don't advocate "don't hire if no OSS". I work with smart people that get stuff done and don't have a Github account. That's fine, it's a personal choice how you use your time.
What rubs me the wrong way is when people say "It's unfair to look at Github as the new resume because I don't have enough time to do open source". Like I said originally, I'm sure someone is going to come along and post about how every hour of their day is being used for meaningful activities, but for the majority of people I don't think that's true.
I remember once a new coworker telling me -- on his first day, no less- that he didn't have a computer at home. He was proud of this. He was a new CS graduate, and for him, computers were not an interest, at all. It was just a job. I asked him what he was into, and it was sports, naturally.
I didn't like that, it rubbed me the wrong way. I probably would have given him the thumbs down if I'd been in the hiring loop then.
Turned out he was a good engineer. Better than that, the sport he was into was one I got into as well and we spent a fair bit of time over the years in our off hours far away from any computers.