As someone who has lived in the UK and the US (and someone that has bought quite a lot of new cars including 27 BMWs and 12 Porsches) I have to say that I much prefer the American commodity approach with "instant gratification". I don't think now that there is any production car made that I would wait four or more months for, i will buy something else instead.
Of course a side-effect of the commodity approach (or maybe it is causal) is that cars here are generally much cheaper than in Europe, even if they are made in Europe.
I am not at all sure that UK motorists do not want to buy in-stock cars, rather it is that they don't have much choice in the matter as there are hardly any new cars in stock there.
Pre-registering in the UK is a complete nonsense, a bit like biannual "new number plates", thank goodness they doesn't exist here.