As the blog post author I'd like to add some clarification here. By "seeing" I meant see them speak at the conference, not necessarily that the things they share in common are things you can see. Commonalities can cover a very wide range of things including, but certainly not limited to, sex, gender, and race. That being said, people who fall into some of these visible minority groups often have a hard time finding role models in the programming community. I think it is awesome if conference organizers can help with that, and do not feel that it is in conflict with also providing the best speakers possible.