Context is true. It's totally different to see someone work _with you_ on a project than to rummage around their commits to project you don't really know. The point is to see how it is to collaborate with someone, and that has to be a first-person experience (or take the word of someone you really value, but that's not what you get form random GitHub projects). And also there are tons of developers who never really contributed much to open source. e.g. in the Microsoft world this is not so rare, and you'll miss these people if you _require_ a GitHub reference...