My 2c as a local: I live in zone 2 and at least anecdotally I am in disagreement with your point here. So I looked it up in your link from TfL - "There are 2.56m cars licensed in London. This equates to an average of 0.3 cars per adult. In total, 46 per cent of households do not have a car, 40 per cent have one car and 12 per cent have two or more cars, with very few households owning more than two cars."
This is the same as your stated numbers, but framed in a substantially different way. In addition I suspect this is dominated by the outer boroughs; maybe one or two of my 20+ coworkers who live in zones 1-3 have a car, it's more once you get z4+.