Earlier quoted context omitted.
This works great if you don't mind cutting down the number of car models a whole lot. Factories are reconfigured multiple times a year to make different models and there's weeks of downtime between manufacturing runs. It might be months before there's a factory that is ready to make a lower-volume model.
In Sweden where I live popular configurations fitting specific price brackets are kept in stock. Custom configurations on the other hand can take weeks or months to get from the factory to Sweden. Those who know what they want pre-order a car so that it's delivered when they want to replace their current car, which is usually every 3 years. I bet Dell still keeps an inventory, it's just a vastly reduced one.
That's pretty common. I can walk into an Apple store and walk out with one of a variety of models. However, many memory and disk configs will have to be special-ordered and I'll have to wait a couple of weeks.
I expect if car selling moved to more of a BTO system, you'd see dealers/factory stores stocking some level of popular model/trim package/color combinations but everything else would be weeks to months to get.