I think you underestimate the false negatives you get with that idea. I can't be the only one who would rather do consulting or hacking at something that might at some point become a startup than doing open source.
And to top it of, I hate github (their functionality should be build into the git client, I shouldn't have to check a web page to see if anybody has ideas to improve my code).
But likewise, after work I'm usually doing some work on my freelancing projects, half of which the client has rights to the source code for, but is not open source.
Getting two "salaries" every month is useful for quickly building up equity.
