If you put a DC current through a stepper motor, it will just stay put in one position, but if you then apply an external torque to that motor, it will rotate a little bit, and when the rotor is rotated for a single full step, then the motor delivers it's maximum torque. And this also works the other way around. When a motor is loaded to way less then it's rated torque, then you can get more resolution by applying microstepping. So you can use the full motor torque for fast acceleration and when the guide rails are smooth you can gain two or 3 bit of extra resolution during the final placement when forces are low.
But there are other things to consider too. I do not know what Neoden does. but the bigger laser cutters often have some extra pulleys and a small timingbelt to get a 2:1 or 3:1 speed reduction, which also enhances resolution. 3 phase stepper motors often have 300steps/revolution, and two phase 400steps/revolution motors also exist. With closed loop motors, you can also get more accuracy, but stretching of the belts is also a real issue. Getting a real 20um repeatability with timingbelts that are a meter long (there and back again) is doubtful. Heck, you probably already have such deviations if the aluminium frame warms up a bit from a motor getting hot.