Yes, I agree, which is why I said "obviously they'd have a case," and wasn't questioning that.

This is an interesting question. I would not agree that checking in is a "statement of intent to travel." Often times, when I check in for a flight 24 hours before departure, I may or may not travel. It depends on what happens in the next 24 hours. In fact, there may be a 0 percent chance of me traveling (on that specific flight) but I'll check in anyway, for any number of reasons (one good one is so that I can bypass long TA lines and go straight through security to the gate of the actual different (earlier/later/different routing) flight I want to standby for.). I see absolutely nothing wrong with that. I'm sure this is completely S.O.P. for many many pax. That is the whole point of refundable tickets and changable award tickets - they are refundable/changable even AFTER departure, let alone check-in, whether you have checked-in or not! A ticket does not magically become "non-refundable" simply because someone checked-in. I see nothing in NW's Domestic General Rules that indicate otherwise. If I missed it, let me know. Someone could even, say, buy a OW ticket for a flight tomorrow, check-in, see if they get upgraded at the gate, if not, cancel using Customer First and fly another carrier or fly the next day, etc. Nothing wrong with that, either, although it's probably more debatable.

I see no argument for the airline using check-in status as a means of determining whether you 'intended' to travel or whether your ticket is refundable. And even if it IS a sign of "intent to travel," that is not what determines whether an airline charges you.

That is no different than if I don't check in. They can't sell the seat right now. If I don't check in, they aren't going to sell my seat. Well, at least until no earlier than 30 minutes before departure when I haven't checked-in and they cancel my seat. The chances of them "selling" any seat 30 minutes prior are slim and none. And this is not a itin. where they try to sell upgrades at the gate. The only thing they may do is give my seat to a standby passenger or upgrade an elite, but no revenue event happens either way. I see no difference in revenue (or even convenience) to the airline whether I check-in or not.

Tons of people check-in for flights and end up not going on them - the airline has an established process for dealing with that that runs on every flight, thus I'm not requiring them to even 'work harder' or do anything out of the ordinary because I'm checked-in but not boarding.

I see no ethical problem with checking in and not flying in this case. But I do wonder whether NW would try to use that as a way to re-charge me for a ticket previously refunded. As stated above, I don't think they'd be right to do so, but that doesn't mean it wouldn't happen.

I do see a problem, as has been discussed elsewhere, with buying a Y ticket just to get into the WC or past security, etc. In that case, you're preventing the airline from selling the seat.