This worm only enfected a few thousand I think but what you have to remember is how small the rate of computers and networks there where back then.

VAXes was used to hold large amounts of data.
You see, if it infected VAXes which was used heavly by large companies and goverment offices that means that this thing would have attacked FEDs and military peaple rather than the usual hotmail user.

It may not seem like much now compared to the code comeing out now days though.