Joules was explanation was empirically correct, but perhaps didn't do justice to "Why you always want to wire the motors in parallel".
First off. The rated current of the motor is fairly meaningless on its own. Multiply it by the rated voltage (which is even more meaningless on its own) and you have a figure for motor power that is a little bit useful in comparing motors.
The reason the rated current is meaningless is that the motor will only actually draw that current at its rated voltage at 0 RPM. The instant the motor starts to turn, the motor current (and hence torque) will drop away. How fast it drops away depends on the most important characteristic of the motor, its inductance.
Now stepper drives do a clever thing, they take your motor with its (say) 5V rated voltage, and apply 50V to it. You would think this would instantly blow up the motor, but the inductance of the coils means that the current ramps up (fairly) slowly. When the current reaches the set point of the drive, it turns the voltage off and the current starts to drop, on, off, on this is what makes that squealing/hissing noise you hear with some drives... Effectively the drive will increase the applied voltage to the motor as it begins to turn maintaining the set current until the motor is turning at a speed that the drive can't provide enough voltage for, at which point the current t (and hence torque) will drop away.
So you end up with a torque curve that looks like this:
What determines the point at which torque drops off are drive voltage and motor inductance.. This is why the more expensive drives can work up to around 100VDC, and why you always want to wire your bipolar motors in parallel.