I think the reason I, personally, need to be able to read DRM books, is for those occasions when you hear about, or someone recommends, a new mainstream book.
However, price will entice me to purchase as well. Just the other day, I purchased a DRM'd book from Robert's site, because I knew and liked the author's work, and it was cheap compared to what I pay for the paper copy. When you're talking about the price of a few beers (or about one beer at some clubs

) then that's almost as good as free !!