Single fans
Motors are funny things, because many of the clean-fan uprights in the UK (though by no means all) had only one moving fan and one static set of vanes, and these were never high wattage motors, nor were they noisy, so I guess it proves that it's possible to make a satisfactory motor with one fan, but as you say, it's probably a costly process.
Another cleaner with only one fan was the Philips cylinder. They used the same motor (albeit with different wattages) for years and years and years in all different models, and this only a single-fan motor. Despite this, the cleaners were powerful, very quiet, and cheap to buy when compared to others.
What I find interesting about anything that is built to keep costs down is that it doesn't always tie-in with what needs to happen. What do I mean by that? Well, prices of appliances in the UK have declined steadily over the years, largely due to the knock-on effect of mass consumerism and mass production, whereby a product becomes more desirable so more people purchase it, and this in turn brings prices down as manufacturers mass produce it and save money, and on it goes.
But into this we had imported goods which often sold for less than anything made in the UK, so that brought prices down and pushed competition up. But it was certainly a steady change. However, since the late 1990's when recommended retail pricing from manufacturers was outlawed, and with the internet coming to fruition, prices have plummeted. Did consumers demand this? I am not sure.
Cheap can be very dear. The only time anyone wins now is when they hand over money for a new appliance. Everything else is a loss. Practically everything seems to be made in the Far East now, nothing is repaired any more, so many local shops for all types of appliances have closed, major retailers like Comet have gone bust, and appliances of all shapes and sizes are bought with the knowledge that they won't last very long at all. For the price, they are still good value in by opinion, but that doesn't solve the problems of course.