While I don't doubt that Facebook has already peaked and will experience some drop off, I don't think the method used here is as valid as in years past. The typical user will just type "Facebook" into the address bar of a computer and click on the first result that their search engine of choice returns. Or at least that is what they do when using a traditional computer. However, everything has been moving towards mobile apps. The only time you are going to search on your phone or tablet for Facebook is once in your app store. Even Facebook has admitted that this is the trend, so they have been pushing to monetize their mobile apps. Just a quick look at the Facebook App in the Google Play store and it says that it has been installed 500,000,000-1,000,000,000 times. One can assume the same thing for the iTunes store as well. That is a lot of people out there who aren't typing "Facebook" into a search engine that this study are not going to identify.