[bombcar]

It can be a lot easier to fill a train if scheduled right between a 20k city and a 1 million one - as the people in the 20k have real reasons to not live in the 1m and still commute there. But if you're looking at 5m vs 20m the "city" experience will be similar so ... why not move to the city you work in?

[Macha]

It's almost like I gave a second example that's not a commuter town for this exact reason.

[iso1210]

People travel for reasons other than commuting.

[bombcar]

Certainly, but if you look at the percentages, the easiest way to get to consistent usage is to use commuter. "Business" can be considered as a superset of commuter, short irregular business trips, but that's harder to build an entire line on (it can certainly be an upgrade to an existing line).

The second easiest is feeder - for example if the line between cities includes the airport, etc.