I guess I'll throw my hat in the ring.

The simple answer is the voltage on the gate of the FET creates a charge. It's this charge that turns the transistor on or off. No gate current is needed for this action to occur. Since no current flows through the gate the gate doesn't draw any power, as power requires both voltage and current (P=VxI).

Kind of like if you put a charge on a balloon by rubbing it on your head, your hair will move towards the balloon without any current flowing between your hair and the balloon (no power required).

A bipolar transistor (base, emitter, collector) is functionally similar to a FET, but it's base does require current flow and it's internal operation is very different than the FET.

One thing to keep in mind. If a voltage is applied it has to be referenced to some point. If the low side isn't specified then it's implied to be ground (or the lowest potential in the circuit).

Think of a battery. If you only connect the (+) terminal and leave the (-) terminal floating, the battery won't do anything.

In the case of an n-channel MOSFET, the connection on the source acts as the low (-) potential and would provide the current ('ground') path you're looking for. Even though the MOSFET gate doesn't require any current to operate, it still needs the voltage (potential, charge) difference between the gate and the source to turn on.

In electronics, I think it's helpful to understand that the components don't know what "ground" means, their operation is only based on the potential differences between their connections.

Don't know if this makes things clearer or more confusing.