So what's the point of making a GitHub if you're not going to publish source code? Is this an inside joke?
Also assuming something on github is the official repo is dangerous anyway. There might be multiple repos with the same name, there might be a more actively developed fork and the official one might be unmaintained, etc.
So... this doesn't hurt, and can definitely help. It isn't perfect, but it cost JWZ very little to do.
Why are you arguing against it?
The code is not there, but the jwz has a github repo saying it is not there: https://github.com/xscreensaver-official/xscreensaver
As for "happens every day". How often, really? JWZ says "I strongly recommend that you install a binary package rather than compiling it yourself." I would guess very few end users compile xscreensaver themselves.