Nonsense. The variance from battery voltage is insignificant. What's more important is that there's a 1.5-2V spread between observed battery voltage vs alternator voltage. That really helps give early warning of problems. For example, it prevented me from driving off with an open field winding, a fault which can't be detected by the idiot light circuit.

Do you really think this is uglier than a gadget sticking out of the lighter socket? To each his own.