The header is not true.  However, Twitter usage is shaping up as significantly different compared to other social media.  According to Harvard Business Review:

Twitter's usage patterns are also very different from a typical
on-line social network. A typical Twitter user contributes very rarely.
Among Twitter users, the median number of lifetime tweets per user is one. This translates into over half of Twitter users tweeting less than once every 74 days.

This is very very intriguing.  First of all, Twitter is growing faster than any previous social media property, in terms of users.  Look at this graph from Compete:

Yet, the new users are not tweeting.  The median number of tweets is 1!  This is mindblowing.  To me, this makes Twitter look more like a TV broadcaster than a true social media property.  These 20+ million Twitter users are all following Shaq and Ashton Kutcher, and maybe that's it.

The only business disruption of Twitter so far seems to be its assault on RSS.  Even with Google Reader, RSS had never broken into the mainstream.  Maybe it never will.

UPDATE: Jeremy Liew's picked up the same point and also remembered that Nielsen reported on Twitter's poor retention track record.

Currently, more than 60 percent of U.S. Twitter users fail to return
the following month, or in other words, Twitter’s audience retention
rate, or the percentage of a given month’s users who come back the
following month, is currently about 40 percent. For most of the past 12
months, pre-Oprah, Twitter has languished below 30 percent retention.

I don't want to sound like a Twitter bear, because I am not.  I think Twitter's an example of the exciting opportunities the connectedness of the internet opens up.  However, we tend to group many things under social media these days and I suspect we're bundling models with very different characteristics.  I am trying to digest and understand the taxonomy and recognize the patterns.