I tried to put myself in the place of the manufacturer of a fan. I know many potential customers won't need fancy features raising the sales price, so I want to offer a complete package as cheap as possible.
On the other hand, I might put in a nice feature — if it doesn't cost too much. Adding one resistor and one capacitor allows for both DC and PWM control, a feature that will do well in advertising my product, without significant rise of the production cost.
If the customer wants something fancy, it’s his job to provide the circuitry. As for post #40, there are several mistakes in one circuit.
The IRLB8721 might just work. Now you’ve got 4 components. To make the fan go slow, use analogWrite(pin, 254); and to go fast analogWrite(pin, 1);
[Edit: symbol corrected]