It's an oligopoly, and the term that you're looking for to summarize "changes in service and price do not change utilization much" is "inelastic". Air travel is

It's an oligopoly, and the term that you're looking for to summarize "changes in service and price do not change utilization much" is "inelastic". Air travel is interesting, because I think it has a sigmoidal elasticity curve - there are a lot of people who simply must fly, a good quantity who will fly if it is affordable, and people who will fly any time anywhere for a cheap enough ticket. This is why airlines have so many classes - to get the low elasticity travelers to pay as much as possible, while getting as many high-elasticity travelers to fly.