[Writing] On commercial success

Well, not my commercial success, obviously, because no one seems to want to read my scribblings so far, but about Dan Brown's. I spotted a thread on the SFFChronicles board where someone mentioned that his new novel, The Lost Symbol, has an initial print run of 6.5 million copies. That's a lot of paper.

On the board, a whole debate ensued in which some claimed Dan Brown is unable to write decent prose - and the undertone there is clearly that he does not deserve this success because of this perceived lack of skill - whereas some others claimed his prose is simply not "up to literary standards" but because it is so successful, you cannot uphold that it is "bad prose".
I tend to agree with the latter opinion. If he sells so incredibly well, he must be doing something right. For the masses at least. For a novel to become so popular, it must touch a large section of our population in a shared psychological soft spot, and the writing must at least be good enough not to detract from the story.

I feel that to malign people like Dan Brown, Ian Rankin and others who were mentioned on the board as "bad writers" is a little sad - especially when the comments come from unpublished or relatively unsuccessful (commercially speaking) writers. It always sounds a little like "I'm not enjoying this huge success but that's because I don't want to stoop so low, I'm a much better writer but the masses don't get, and the agents don't get it because they're all so focused on bestsellers...".

What do you think?