I agree with all the arguements about what a worthwile, strenuous and beneficial activity trainer riding is. But that still does not mean that it is miles on a bicycle. If I climbed Mt. Everest or swam the English Channel it would be a great physical and mental feat. But in the course of doing it, I would have logged exactly zero miles on a bicycle, same as when I ride my trainer.
But then, the only meaningful measurement to me is not miles or speed or time, but holes in my belt.