Some people are all in a twist over the news that most of Kindle's top "sellers" are actually free--nine of the top 10, 64 of the top 100. But is this surprising? Seems to me it is just what you would expect. If a clerk leaves a bowl of free candy next to the check-out counter, it will be free before the clerk goes on her next break. The only difference with the Kindle is that the candy is probably more expensive--recall that the marginal cost on all these books is effectively zero. Granted that the sunk cost has to be something > zero, but I bet not much, and in any event, I bet Amazon ain't payin' it.
Anecdote as data: I scroll the free stuff from time to time, have added a few, have knocked a few off for space reasons (all free, what's the big deal?). I've also bought about 70 books over the year since I got it. I don't know how many I would have bought in paper but I know it is not 70, so Amazon has squeezed something out of me. I suspect that maybe none of my 70 is in Amazon's top 100, but I do suspect my dollars are just as green as anyone's else.
Afterthought: have you any idea how handy it is to have a Complete Shakespeare on your Kindle? Never at loss to complete a quotation. Or for solace in a dark moment. Not very well edited, but good enough, and hey, it's free.