It's because you wrote above "the train stations consume between 15 and 80MW". And the number of trains has no effect with the power consumption.
I just tried it out with a separate power line. I have a train line with two stations, two freight plattforms and one train. My Powerpole says:
1. each station consumes 50MW all the time (=100 MW all the time)
So it's not the station consuming 15 to 80 MW.
2. each freight plattform consumes 50 MW, but only if they're active (loadung/unloadung)
3. train consumes what it needs (from 15 MW to 80 MW), but 15 MW all the time, even if it stands still.
4. Alltogether it is a power consumption of 115 MW in idle (no train goes, no plattform loads/unloads).
5. Putting a second train on the same track rises this idle consumption to 130 MW.
So everthing works as intended, at least in my game.