orbitmic

I can't direct you to the specific threads because I don't have time to look for them, but as brunos says, some of the threads on various airlines fora were rather specific in the details, including, (1) cases of people reporting their TA having been sent memo debits, (2) reference to an article in Business Traveller about a European airline cancelling a member's FF account and all miles earned because of him/her repeatedly skipping the final segment of his/her trips (as well as airline's own comments and Business Traveller's editors' comments that the airline seemed entitled to do so), and (3) reference to people explaining that their FF account was indeed audited and that they understood that skipped last segments was what had triggered that, and the result of vast amounts of miles withdrawn from their account.

Now of course, these are not court cases which you can externally verify, but they are all specific statements by people talking of their own experience on FT and in reputable magazines, airlines' answers and magazine's comments after looking into the people's cases and contacting the airline. I would say that it is at least as evidenced as 99% of what is discussed/commented upon on FT.

In the same threads you will also find a description of the logic which details why the argument you make that this is just equivalent to not using something that you bought or skipping a course in a set menu is probably NOT legally tenable (in a nutshell, because IATA rules and CoC systematically and consistently state that you don't buy a series of coupons, which would indeed give you a right to use some and skip others, but a full itinerary from point of origin to point of arrival and/or return, which means that if you fly JFK-CDG instead of JFK-LHR -- regardless of whether your routing was via CDG or not -- you are basically helping yourself to the lobster while you paid for the cod). This is how plane tickets are conceived and sold, how they are protected (e.g. by EU regulations), and how they are enforced (for instance in the case of reroutings). The German court ruling was indeed not about a last segment but nonetheless fully support that logic: somebody bought an LH ticket with connections but skipped an outbound segment. The airline cancelled the rest of the itinerary and it went to court. The court ruled that the airline did not have the right to cancel a passenger's itinerary but was entitled to reprice the ticket according to the itinerary flown by the passenger. This suggests that they agree this is no 'set menu' or else there would be no reason to let one skip dessert but not the starter! Note that you are allowed in any case to not consume what you bought (ie not fly at all).

Would airlines sue for someone skipping the last coupon? No, they would be stupid to do so as it would invariably cost them more money (plus reputational capital) than it would bring considering the cost of legal action. Instead, they choose, "easier" ways such as threatening to refuse to return one's luggage until difference has been paid (see irishguy28's point above, although I personally doubt that such 'hostage strategy' would be legal), sending TAs debit memos (if TA refuses, then sums will this time typically be large enough to justify legal action) or cancel FF accounts and or significant amounts of miles (specifying in their own T&C that not behaving properly including not flying all coupons in the order they were booked can cause this makes it very easy to them).