Sure, I'm dramatically oversimplifying, but I think my point still stands: putting it another way, trains have an ability to accommodate travelers in a way that nothing else -- planes, cars, buses, etc. -- can even approach. It wouldn't be as easy as I'm making it out to be, but it also doesn't seem (in the larger picture) to be particularly challenging either.

And you're right, you'd probably have to designate a section of the train as the "getting on and off" bit, and make it easy for people to move from car to car.