Quality is subjective. Call of Duty has a very high quality because people want to buy it and enjoy the game. Having high sales means developers will take more time and money to create add-ons and sequals as well. What seems high quality to you may not be high quality to everyone else. Uncharted might seem dull and boring to Call of Duty players.
If you add up the utility from higher selling games and multiply it by the amount the game sold you would find that people earn more satisfaction from the highest selling games rather than the lowest selling games. Most of you will derail my thread because you're not educated. That is how I determine quality. If you don't know what I am talking about look here. http://en.wikipedia.org/wiki/Utility
No sales = No game = 0 quality = DOOM
Some sales = cheaply made game = some quality
High sales = high budget game = High quality
Sales is correlation with Quality
If a crappy Gears of War/God of War came out (like they did in 2013), they will recieve less sales (which was true).