The product was the answer to what THEY needed. Add to it a very strong viral marketing component. In addition to their creativity, they were also extremely technically smart. The clever architecture they developed within only four months was able to maintain over one million concurrent users. So far, other than ICQ and AOL no one has been able to accomplish such a feat.
Many pundits describe convergence of technologies, others divergence.
Different horses for different courses. There are issues of different levels of urgency, invasion, latency. Sometimes you want it one to one, sometimes one to many, sometimes many to many. Different means offer different choices. I think what we will see intervergence - different means will keep their basic forms, but they will be able to be fetched in different modalities from the one they were sent in.