Twentyeleven customizations a lot of blogs seems to use

I’ve recently noticed a bunch of blogs using basically the same customizations for Twentyeleven and since I like the design I’m wondering if it’s a child theme or how they just seemed to end up with similar looking themes?

http://www.fourhourworkweek.com/blog/
http://www.marksdailyapple.com/
http://freedombusinessblog.com/