How does it not work? It works fine. You can't ask for your money back when a movie sucks, you can't demand that an artist change the song because you don't like it (well, you could, but again good luck), and you can't demand your money back from an author because the ending blows.
The obvious is that it's subjective. I like the ending to ME3 because it leaves so much of what happens up to my imagination and doesn't have to spoon feed me every ounce of closure. More than just being subjective is that it's art. You pay to take the risk on something, and if you don't get your money tough. However, art works on risk. We all like our franchises but what about that first initial purchase. No matter how much research you do there's always that element of risk involved. It's why there are fans in the first place.
Who says you can't ask for your money back if a movie sucks? I have. I've walked out of movies that have sucked (after the first ten minutes, I didn't stay and watch the entire thing) and demanded a refund and was given my money or given free tickets to another.
Books, music and games all are sold with the idea that there's no refunds because by playing them, breaking the furrow or tearing off their shiny wrappers their value has degraded. So asking for a refund for a book would be like asking for a refund for a game because it doesn't have the 'newness' of another. But I don't think that's true because games look they same no matter what and if they're in mint condition they are just as valuable as the one on the shelf. The only one who is telling you it isn't is the industry who doesn't want to give you a full refund for a game if you are dissatisfied.
Don't get me wrong, I'm not up their every time trying to get my money back on every game I dislike because of awful mechanics or too many bugs or because the content failed to live up to my expectations. If that was the case I'd never buy a Bethesda game ever again. But as a consumer I have the right to say, 'This product didn't deliver an enjoyable experience. It didn't deliver the RPG experience it promised. The ending was terrible and I would like to see some more options.' I have the right to tell Bioware that and so do any others who felt the same and supported them from ME1, hell anyone who bought the game can say that. I didn't expect there to be DLC to change the ending but I'm glad there is. I'm glad Bioware and EA have the decency to realize some folks weren't pleased and they are attempting to make that right with consumers.
Isn't that the type of world we all want to live in? Where we have some say and aren't just expected to take everything and pay hard earned cash for a product we aren't satisfied with? I don't know about anyone else but I work damn hard for my pay and I'm not going to just give it up for a product, game or otherwise, where I feel I receive less than what I paid for it. I can appreciate the 'art for the sake of art' argument but even artists know where their patronage originates and play, paint etc towards their audiences. If they didn't, most of the great works of art from the Renaissance and the folowing periods wouldn't exist.
You're part of the group who liked the ending, that's fine with me. I can accept your POV about why you liked it. I find there's a tendency among people who liked the ending of ME3 to run-down or try and malign fans who didn't. I don't know why that is. I've had people say 'well it's war it can't be all puppies and daisies..' I didn't ask for a puppy or a daisy.