This is indeed the holy grail of Word of Mouth marketing - finding influencers, who can start a trend. Indeed, Keller Edward has also written a book on them - The Influentials.
However, there is a contrarian view too, and read more about this on Fast Company, in this brilliant article 'Is Tipping Point Toast' - http://www.fastcompany.com/magazine/122/is-the-tipping-point-toast.html
To summarise, what Duncan Watts is stating here some ideas stick whereas others don't has less to do with people who propagate them, and more to do with society's preparedness to accept the idea. 'No army in the world can stop an idea whose time has come' - as Victor Hugo famously observed.
So, we always knew that, what's the fuss about? The point is that if Duncan Watts is to be believed, then it takes the wind out of Word of Mouth marketers' sail, because all trends become highly random, as they appear in the first place. So, marketing dollars will leave the glamourous fashion / trend creation budget and go back to old fashioned market research. Makes sense, isn't it?