Remember there's a difference between a head bolt heater (invented in Grand Forks, ND, circa 1940) and a block heater. And neither is the same as glow plugs for a diesel. A head bolt heater is trying to keep the engine coolant warm (yes, oxymoron). A block heater is keeping the oil in the pan warm. The goal of each is warm the engine enough to allow for an easier crank and start.
Modern engines, and specifically modern fuel injection systems, have really made cold weather starting much easier. Old carburetors didn't do well in extreme cold.
Another factor for easier starting modern engines? Back in the day it was a 351 cu in (about 5.7L) Windsor V8 in a Ford LTD. Today it's a 1.5L (about 90 cu in) to 3.0L (180 cu in) engine in most cars. The battery size (physical) is the same; the battery tech is literally decades advanced. So, more battery 'gusto' and half as much 'engine' to crank over.