What the author of the article fails to understand is nothing lasts forever on the internet.
Facebook can become insignificant 1 year from now just because a new service propose better features at a lower price, or just because people get bored...
People used to have email accounts at yahoo , yet , people now prefer gmail because it is easier to use and is less "spammy".
People used to have myspace accounts , and guess what, moved to facebook...
But it's also true that nothing's free on the internet. Twitter is not free , neither is facebook , and as a business they need to generate revenue.