Mitch nails it as usual.
In a global conversation, your customers are not only being satisfied or dissatisfied, they are talking about their experience. The reason to operate a blog in support of your business is that if you aren't involved in that conversation you are both deaf and dumb in the market.
That's a hard message for many to hear, especially those marketers who believe that their work turns mostly on the placement of massive investments on a conceptual chessboard. The blogger to some degree becomes part of the story of a product or service, supplanting the traditionally clean image of the company with a more human one, a face that people can praise and attack. It's hand-selling in the same sense that retailers strive for, where an individual's passion for a product (a book, a piece of software, or a car) is translated into a sale because of a conversation in the store or showroom.