I was going for whether it's legal not whether it makes sense - but no-one in their right mind takes legal advice from a random internet poster anyway so I'll stop here with that line of argument.

Airline ticket pricing is far from intuitive. It's best to think of tickets as perishable, finite products. Once a seat flies unfilled, it has no residual value at all. Its scarcity value (as more seats are sold, the unsold ones become more valuable) goes way up until it's wheels up, then it has no value.

If they knew that you were only going to fly one way, they (a) would have priced the ticket so that they could hedge the risk of the seat not being sold on the return portion of your ticket, or (b) offered the "return" seat to another passenger who would buy a discounted advance-purchase round-trip fare, or - even better - to a "walk up" passenger - say business person - who didn't have time to plan in advance, for a much, much higher fare. Your no-show didn't give them the opportunity to do either, i.e., net "opportunity cost" to the airline.

As a practical matter, they probably won't bother with you, as they deliberately overbook anyway, expecting a certain "leakage," and can allocate your seat to a standby.

If you multiply this times umpteen million passengers, the result you get is Ryanair and easyJet. No perks, mainly one-ways sold, via airports in Yenevelt. Oh and don't forget the extra €s £s and $s needed for bags, water, etc.

Why not take the train for 39€?
By the time you pay to get to the airport from downtown Munich and into Zürich from the airport, you will have paid about 3 times that amount.

Changing the OP's question slightly, the consensus here seems to be if you miss a leg prior to the last flight, they'll cancel the remaining flight.

Earlier this week I was comparing an open jaw ticket from Dulles to Munich, returning from Frankfurt to Dulles - which was more expensive than a R/T out of Munich, with a layover on the way back in Frankfurt. Based on the previous posts, are you all saying that there's no real way for me to skip the Munich to Frankfurt leg, and just pick up the flight from Frankfurt to Dulles, because the airline will have already cancelled me?

kgh8m - That's correct. Do NOT try it.