However the scope and history of social media is much richer and deeper than this.
PeopleBrowsr recently commissioned a cartoon history of social media, which starts with the first robot messageboard - in 1930.
Even this cartoon merely skims the surface and doesn't go further back to pre-digital social media channels that existed before the 'big three' traditional medias grew up during the 20th century (newspapers, radio and television).
However it does go deeper than the Twitter/Facebook view of the social media universe.
For a commentary on the cartoons, visit the PeopleBrowsr blog