anyone who sets up their speakers with just a tape measure is a moron imo. the guy you're talking about seems to really know his stuff. if you're a OCD audiophile you might not be able to handle the sight of your speakers not being exactly the same in a perfect triangle of some kind.. i would say try not to restrict yourselves in this way as you will also be restricting your hi fi.
Tape measure (or better, laser measurement) is very useful, and I employed precise configuration based on that to obtain significantly improved presence and palpability of sound images. So I would be the last one to dismiss it, and I would recommend it as a very good starting point. However, as you suggest, it is no absolute. With perfect geometrical alignment my center image was not precisely in the middle. So I moved the left speaker back an inch and, voila, the center image was spot on. That small trick to get the center right, moving one of the speakers back or forth a bit, is actually described in the manual of Genesis speakers.