[pminmo]

So if I add a shunt resistor to do current sensing and regulate the current within the range of the motor with pwm I should be okay?

Maybe, it's more complicated than if your doing a bipolar driver and want to do microstepping. Decay modes become important and need to be addressed.

As was addressed by others the reason for higher voltage is to increase the speed attainable by the stepper. If you look at a stepper motors torque verses step rate, you will see it's torque drops significantly as step speed increases. As you increase the motor supply voltage, the rate of drop slows.