Yup, the latest bestseller does not win the Booker prize.  And even from a commercial perspective, it sort of works in the long run I think.  First, because the really good stuff tends to have a long tail--people keep on slowly buying that stuff for years and years with no further effort on the publisher's part.  Whereas especially nowadays, every bestseller pretty much has to have a full-court press of publicity, which costs a bundle, and for your trouble you get a big whack of sales for a few months and then nothing, and you have to do it all over again.  More subtly, particularly in an era where the basic idea of reading a book as opposed to surfing the net often seems to be in trouble, it's probably a good idea to keep the intellectual "cachet" of books strong.  The point of literary prizes isn't to sell that particular book, it's to sell the idea that reading books == intelligence, education, sophistication (and so people with aspirations to such should go around reading them).  Even in the US there are quite a few people who value that kind of vibe, and most other countries have less anti-intellectualism than the US does.  For that, you need to have intellectual sophisticates picking impressive, intellectual, sophisticated books.