The increased torque does have to do with the fact that it is a digital. Digital basically just refers to how it pulses the motor I believe. Analog servos pulse the motor at a fixed frequency and vary the pulse width to increase torque/speed. Digitals pulse at a much higher frequency and also vary the pulse width. This means that digitals deliver more energy, quicker so you get better speeds, more immediate torque and higher torque. The downside to that increased energy delivery is quicker battery depletion as was mentioned. The link that Barracudahockey provided explains it much better than I probably am.