I find it curious that they attribute the "start" of the Internet to 1991. One of the Internet time lines suggest that 1990 was when dialup service was first commercially available (see http://www.zakon.org/robert/internet/timeline/), so perhaps that's the rationale?
the rationale is probably that it became legal to route commercial traffic over the mainstream internet at around that date. ;)
I'm not familiar enough with these other diffusions to know for sure, but it seems iffy that the others had the same kind of non-commercial incubation that the Internet did, so a straight comparison may be misleading.
right - most of those things had commercial sponsors pushing them along. i just did a little googling and found this paper, specifically relating diffusion of innovations methods to the early internet's development: http://www.au.af.mil/au/awc/awcgate/innovation/adoptiondiffusion.htm elijah