Facebook as a Standard
Facebook has grown to a point where its user interface decisions are not only impacting sites within its vast ecosystem, but also sites on the periphery with overlapping characteristics.
Like it or not, Facebook is setting the standard for social networking design.
Standard: 80% or more of websites use the same design approach. Users strongly expect standard elements to work a certain way when they visit a new site because that’s how things always work.
– Jakob Nielsen