"These sins have been compounded by external factors - the decline of book reviews and the halving of the number of independent booksellers from 4,000 to 2,000. What publishers don't understand is that media blitz campaigns are often less significant than old-fashioned word of mouth, which is disseminated patiently and slowly through book stores. Books are not Hollywood, to the general astonishment of agents and corporate suits. They are intimate, unpredictable agents of delicious rebellion."
Read more here, although I’m not sure I agree with him on everything.