First off, it's kinda silly to base awards on album/single sales, as they've already gotten their reward for that. Secondly, they explicitly state that they're not based on sales in any way, which is obviously untrue. It's not as if they specifically recruit high-sales artists for the Grammy nominations, I'm sure, but those that have higher album sales have higher exposure, which means more people will vote for them during the nomination process (about the procedures of which I'm making assumptions), so you effectively get sales-based nominations. That is to say, if someone made an album that everyone who heard it thought it was the best album ever, but very few people heard it (probably because it wasn't promoted in any way), it wouldn't get a Grammy nod. And there are way too many albums that come out to expect even a person who goes out of his way to listen to a lot of music to have heard all of it, and I doubt that most of the nominators have really listened to all that much.