I think games sales matter a lot. I just think that the people who should worry about sales are the people who have vested financial interest in a game. If your money or livelihood is dependent on a game, then you should concern yourself with its sales. But if it isn't, then you should try to relax and just enjoy playing them.
...And that's why, unless it's your money on the line, game sales don't need to keep you up at night. The market and game executives do not dictate what games get made—They just dictate what gets made easily. They affect what can be made without a fight. As long as there are creative people out there willing to fight for ideas they care about, then there is nothing that the market or anyone else can do to stop them.
Truth. Though, if people didn't worry about game software sales numbers, whatever would people argue about? Probably the gameplay!
Read Schafer's full blog post on this — which also includes his pulled pork recipe. Mmmm pork.