how many ppl actually buy POD books?

hello,

I wonder ... how many people actually buy print-on-demand books? And how many of that number are sincerely re-selling them on amazon.com? I have conflicting numbers - xlibris / Authorhouse only record books sold via them, and not via online distributors like amazon or bn.com; whom resell tens of copies or more per quarter. who are trading the books - and not reporting sales? Is it in the system?

M7 2006.
:P