This puzzles and intrigues me...are you saying that publishers intend for some of their books to be bestsellers, as opposed to all of them?
Everything Karen said about marketing is exactly right, as far as I know. Not just that, but the NYT, for example, doesn't even track the sales of all books; only those it has been notified are potential bestsellers. (Yes, this blew my mind too the first time I heard it.) And it requires a minimum first printing, as well as, in most cases, prominent bookstore placement (which publishers pay for) for a book to have even a chance of hitting the bestseller list.
I'm not sure, but I think this is why you sometimes see bestselling books getting cover changes. Because once the publisher has spent that much money on promotion, even a bestselling book can be thought to be underselling.
I haven't read them, but I assumed they were bestsellers -- because I heard them being talked about all the time.
I think they did get talked about a lot on the book blogosphere (another promotional tool to get a book on the bestseller list is a very large ARC distribution). But even though the book blogs loom so large in our minds as authors, as far as I can tell, they don't necessarily translate to bookstore sales. I read somewhere that about 50% of book sales are impulse buys, which is probably why book placement in stores is so crucial.