I agree with everything else, except this. I suppose that it depends on how you define "often". I don't remember steam (except the heritage railways), and was born in the era of blue diesels, but they are the last thing that I want to model; people take different approaches to deciding what they want to express, and how they want to express it.
....and the other factor in the 'people model what they remember' theory is that people's memories of the railway will vary- if you grew up in an area that had suffered heavily from the Beeching axe, then your childhood railway memories, and their influence on your railway modelling might be very different to someone who grew up in the Southern Region commuter belt, or close to the ECML/WCML.
Growing up in a town that lost passenger services a couple of years before I was born, my railway memories probably involve as much time travelling on heritage lines as they do BR, so my modelling has been pretty steam-centred from the start.
If I was ever going to go D+E, it would involve lots of 20s, coal wagons, NCB diesel shunters and queues of Oxford Diecast cars at level crossings, because that's pretty much my main memory of the 'big railway' from when I was a kid