Earlier quoted context omitted.
Or, as is already the case with a lot of us millenials: We have fb. Everyone we know has fb. Everyone we get to know is added to fb. There is no distinction between private life and work life. Fb is where we keep track of who we know. Fb is where we ask around if anyone knows of a company looking for a person. Fb is where we ask around if any person is looking for a company. Fb is where we group text. Fb is where we…
Don't be so sure your experience matches everyone else's. The 'we' you mentioned does not include me. I will add all my work contacts on LinkedIn but I will only add a few (about 5%) on FB; ones who I socialise with outside of work.
It seems very customary to add at least everyone on your direct team to Fb though.