I think you've hit the nail on the head with your final point. As programmers, you can point to your Github repo as your resume. In the design industry, they don't care about your Github repo (or will even understand it), and they'll bug you about some part of the program that you didn't even contribute to or were responsible for.
I've just heard about 37 signals this past month or two and am thinking about putting out a portfolio for them. Would they actually care about OS projects as a designer?
