According to this Gamespot article, that is how many sales it did:

http://www.gamespot.com/news/6263057.html

Now, not sure if that it through to the customer or just on the shelves.  This site has the total sales at around half.  If this is true, it is interesting to see what other games that people rave about here don't match it in sales.

I think this finally proves sales = quality, hold on wait, wtf?

It proves that... what people want, themewise, etc... is greater than quality.  Quality is how you execute the delivery of something.  You can have poor quality and execute not well, or great quality and execute real well.  Considering that Avatar grossed over a billion dollars, and is a cultural phenomenon, it makes sense that it would sell well. 

You can't just saying "Wow, that is high quality" if it isn't something that naturally grabs the interest of someone.  People don't play quality. They play things they enjoy that hopefully HAVE high quality.  So, let's say Alan Wake ends up bombing.  People here will go WTF? and wonder why the heck the world can't see its brilliance.  Well, maybe people just are not that into "psychological thrillers", and there isn't much you can do about it at all.