PC were sold into the mass market where the 120v receptacle was the norm.
Noise tolerance got a whole lot better by the end of the 70s too. TTL logic had a lot to do with it and CMOS was even better than that. IBM removed all of the requirements for IG and such in the early 80s. We stopped "zap testing" machines on installation and they stopped worrying about star grounding. The modern switch mode power supplies have such a wide mouth that we don't even care that much about sags and spikes on the input voltage.
A lot of the things people "know" about noise and power problems in computer rooms aren't really urban legends but they are mostly ancient history. In my last 15 years at IBM I have to say, every time we "fixed" something by correcting a power or noise problem, we were back in there finding the real problem soon thereafter.


Greg Fretwell