I would assume it has something to do with information hierarchy. The more important elements are bigger, bolder, darker. If everything is this way there's less

I would assume it has something to do with information hierarchy. The more important elements are bigger, bolder, darker. If everything is this way there's less means to draw attention to important information. EDIT: I can't tell actually if there's differences in color between the headings and body text in this case. If not... shrug