I've just been looking at specs on stepper motors - they give the winding resistances as well, 12V ones vary as low as 20 ohms (0.6A), but a 5.3W one is listed at 47 ohms, and a 2W one at 120 ohms.
Where did the stepper motor come from?, I've often taken them out of 5.25 inch floppy drives - I've never measured coil resistance, but they work fine on 12V.
Your confusion with ohms law is because you are expecting 12V to the motor, with the current limited - this is impossible - ohms law is nice and simple, and it works - ALWAYS!. If you limit the current to the motor you are simply reducing the voltage to it. I would be inclined to try running it off 5V or so and measure the current it takes, and seeing if it runs warm, particularly when it's locked in a stationary position.