If you look at the power lines, they are distributed with very high voltage. The reason is to minimize power loss. The power loss in the lines is the current squared times the resistance of the lines (power loss = I*I*R). Since the loss in the line is current time the current, they raise the voltage very high to minimize actual current in the lines.
If I was going to use one main power supply to drive all of my lights, I would want to do the same thing. I would probably pick 48Vdc and feed it through the Ethernet lines along with the control signals. This would be very convenient and would simply wiring. However, this would require me to buy twice as many power supplies, first a high voltage 48Vdc power supply and then local ones at my lights. Since this doubles the cost for power supplies this is not very attractive choice.
The alternate solution would be to minimize the resistance of the line. This requires me to buy very large gauge wire to run power to my lights. With the cost copper being fairly high, this also is not an attractive solution.
The obvious choice for me is to use the normal house power to distribute power to each of the lighting elements.