I guess it's fair to say that fires have changed over the centuries, and the electrical installations have changed too. We used to have buildings made of brick,stone,wood and slate, but now we have all sorts of materials in there including plastics,cladding, artificial wood-based products, and of course where most buildings 50 years ago had maybe mains electricity and a telephone or two we now have multiple extra cables never envisioned before for computers, telecoms, alarms, cable and satellite TV etc etc.
Also, some of the modern building methods, where every component is designed down to a minimum, means that premature failure can occur if not installed correctly. For example, if you have a house where the ceiling and roof joist are of the engineered "I"-beam type and you drill through these to run services, they are prone to failure even without a fire. Where the upright web is typically 6 or 8mm OSB, you can't expect this to have the fire-resistant qualities of a four by two. Yes, wood burns, but solid timbers in the old style will last longer before failing...and that's just the tip of the proverbial, imho.