Its even stupider though to assume the choices people make are stupid. You're not going to win the Hawkings prize if you're going to go around calling people out for their choices and how they live their lives if that has no negative impact on others.
Well, it's an exagerration, but the majority of people (mainstream) will not invest significant amounts of time in all aspects of their life. As you say, if it doesn't have a negative impact on their lives they won't invest as much time. We all make stupid decisions in different areas of our lives because we can't learn everything is what I'm getting at. For this reason, going by sales alone is not a good indicator of quality (especially for experienced gamers on this site who are likely more critical of faults).
Experienced gamers are likely to find fault in areas where someone who is more mainstream likely doesn't. That doesn't mean that the games experienced by the latter are any worse than the games experienced gamers like. Infact in my experience it is the experienced gamer who would be more likely to overlook basic intangible faults whereas someone who doesn't play games as much isn't as likely to accept them, things like bad controls or confusing level design. For instance SMG2 camera angles and level designs make platforming a lot easier in 3D than most platformers, however no core gamer really picks up on that fact conciously.
I'm pretty sure most core gamers can recognise a bad camera angle however. With SMG2, recognition of camera angles may not be conscious, but experience counts for a lot which is why it may not be conscious. If you play a wide range of platform games, good camera angles become an expectation and I think poor camera angles stand out more. If you're a fan of the genre though, you'll recognise but accept these more basic faults thus gaining more knowledge and experience of the genre.
However, in the opposite side, their are a number of games that we can find fault with that have gone on to sell millions. The first Assassin's Creed for instance (which I actually enjoyed) had a lot of basic problems, but it's marketing was done superbly and it did shine in certain areas. Had it not been for the marketing however, I doubt it would have sold as well as it did.
The other point is that smaller games are likely to be overlooked by less experienced gamers. Unless you're actively engaged with gaming news, media and frequent forums such as this one, a number of games will simply pass your radar. I'm thinking Indie games like Galactic Civilisations, Mount & Blade, Darwinia and Minecraft. There are quality titles out there that won't have the huge sales of big budget titles, so I don't see how sales can be any measure of quality when most people aren't even aware of everything out there.
It's like saying Avatar and Titanic are the best films ever created because they made the most money, when there are potentially thousands of brilliant films made every year that most people will never even hear of.