I guess the sense of a rubicon at the end of the 40s was due to WW2, but why at the year 2000? Because phones? Or big round number effect, perhaps? The year 2000 was built up in our minds as when the future was expected to begin. (Every new gadget produced around 1990 was the Something2000. CarVacuum2000, Ionizer2000, SuperShoehorn2000, etc.)