In switzerland someone sued the airline for this
He booked cairo-zrh-jfk as it was cheaper then zrh-jfk. He only got on at zrh. They denied boarding and he had to buy a new ticket. He sued them and claimed it's no difference then buying a package of movies at a cinema and not going to the first movie... it's none of their business, he has a valid ticket for each flight...
Court gave him right, airline didn't appeal, as they didn't want a higher court to make a binding decision, but the court Cleary stated they consider this for the future as well