I thought that they were optional extras that most people just didn't see any point in specifying ... !

Isn't that Audi drivers? ;)

The beauty of English is that when things become commonplace they rapidly acquire a mono or at most disyllabic name in common parlance, e.g. car, dash, rad, air con. Thank goodness German, once the key scientific European language, no longer has to be learned. E.g. Zahnrad, (literally toothed wheel) but simply cog in English. Or the possibly apochryphal story of a tank, or 'sturmpanzerwagen' called a Schützengrabenvernichtungspanzerkraftwagen.

Motoring journalists still talk about the chassis when the majority of modern cars don't have one.

Agreed, maybe the Morgan and some 4x4s but the last in Europe must have been something based on the Triumph Herald and in the USA the Ford Crown Victoria.

For example, they might say the car has 'very taught handling due to the very stiff chassis' when it doesn't have any chassis!

It’s only bad phraseology: VW’s, Audi’s, Seat’s and Skoda’s all share the same underlying structure: it’s only the outer panels that differ. Change chassis to floorplan.

Also people talk about a car's DNA, when cars clearly don't have any DNA.

Of course they don’t. People are just using it as shorthand for its origin or family connection.

Diverging... I once had a Volvo 440 that had a disconcerting way of starting the fan to cool an engine that was not obviously over-hot when I parked the car. I was being taken around a National Trust property when an indignent gentleman stopped the party and asked me to switch off my car engine. I explained about the fan and it's automatic starting but he was not molified until I went out and listened with him to a silent car. (The fan had meanwhile stopped). That fan was obviously not driven by a belt.