But it is not legitimate or fair. If you buy a ticket to C and then travel to B then you have bought a ticket to B at a C price by deceptively saying you are going to C. That in any book of mine is deception and not legitimate at all IMO.

Yes, it is smart of us to find these kinds of things if the airlines allow it I suppose and yes, it is down to them to close any loopholes. However, it doesn't make it right.

I have an OTP-LHR-JFK-LAX-PHX return booked. I am flying my last LHR-OTP because I said I would and the pricing reflected that. I did consider dropping the last leg but I now believe this to be wrong after reading this thread and considering it in more detail. I wouldn't get worked up if others wanted to do it... that is your choice... but for me it isn't right