Obviously I would bow to your local knowledge, I am aware of some people travelling long commutes, but there are obviously lots of villages within London,and lots and lots of houses and flats. With the costs of travel around London being high, I find it difficult to see nurses, bar staff, teachers commuting long distances.Having looked again at your post I think that round trip figure from those so called experts is frankly utter rubbish.
Very few working people live in Central London and one way commutes average about 4 miles from inner boroughs. I know since I commuted from Streatham into both Waterloo and the West End for four years, averaging more that that each way.
From the outer boroughs like mine where such huge nunbers commute from it's far more, I had almost 16 miles each way for nine years to the West End and then 14 miles each way to Wandsworth south of the river for seventeen years.
And these are without the many trainloads and car drivers from all the distant locations far outside London that I mentioned.
The figures you quoted are not just wrong, they are impossible. I suspect they exclude many classes of London commuter.
.