PWM accuracy vs speed control accuracy
Let's not talk about cases like flywheels where the inertia is huge to help stabilize the speed

But we are.  With typical modern microcontrollers and their built-in PWM generators, and typical motors, the motor itself is a flywheel -- not to mention the blade you're putting on it.  Consider this motor, which is designed to have low inertia (and is absurdly expensive for whacking fruit to bits).  It's a coreless motor, which means it has maybe five to twenty times less inertia than a brushless motor.
It has a mechanical time constant, by itself, of 4.87ms.  That means that this absurdly quick-responding motor acts like a 1st-order lowpass filter with a 3dB frequency of 32Hz.
To heap absurdity on absurdity, let's say you're driving the motor PWM with a super-cheap microprocessor like an Atmel 8-bit part, and that for some reason you've decided to use the 8-bit timers.  So you have an effective PWM resolution of 1 in 128.  Even an ATMega will handle updating the PWM at 10kHz -- so assume that.
Now, you've got a resolution of 1:128 -- which is way worse than the 1:500 (0.2%) that you're calling out.  If you simply dither the PWM at 625Hz, you can increase your effective resolution by a factor of 16 -- that puts you well above the 1:500 that you need.  Better yet, implement a simple 1st-order sigma-delta modulator in your software, then you'll extend the effective resolution of the PWM by approximately 300, or a hair over 15 bits.  You could contemplate implementing an even higher-order sigma-delta, but you're already at a ridiculous level of resolution compared to what you need, so why go there?