240 Dual Leg and Return to Source

I'm going to assume you are in the US, because everywhere else, 240V is in fact Line-to-Neutral.

Voltage is just the potential flow of energy from one place to another. It doesn't have to be to ground, it can be from a place of higher potential to one of lower potential. In the case of a 240V single phase supply in the US, it is from either end of a transformer winding and at one end, the potential is at zero volts when it is at peak volts on the opposite end, ever swapping (alternating) back and forth with regard to each other. Nothing more complex than that.

Yes, I am in US and after 25 years have gotten confused about the elementary higher to lower potential flow-- thanks for your cogent and clear reply.