[oposa]

It is a matter of perspective, but I think the more accurate view is that personal travel is what keeps the trains (or the planes) running and business travel makes the profit. You need the "bulk" for flexibility, frequency and maintenance. That is why there are plenty of low cost airlines, but almost no business class only ones.

Differential pricing in itself becomes problem when it comes to something were the value is partly external. Countries that want to maximize utility will have to reconcile with the idea that some of the value won't be captured by the train company. Most countries don't charge different rates for roads, but try to make the best roads and then collect taxes.