This is totally unrelated to rails. This is about OOCss and what's wrong with twitter's bootstrap in this context. The overall conclusion about doing OOCss might be right but there are many other and better resources for this topic- without those bothering meme images.
Surprisingly enough, the first resource I found describes exactly the same example about sass placeholder and %separator http://ianstormtaylor.com/oocss-plus-sass-is-the-best-way-to...