Actually, it's kinda good to tell them so that they know. You know, so that they don't accuse their customers of being criminals when/if their sales plummet.

I mean, every time someone asks me about my ereader I say that it's wonderful for public domain works because there's finally a way to get free stuff for free without lugging around a computer, squinting to read the text on a phone/PDA, rummaging around libraries, or paying lots of money for a print copy. I even point out that the library has lots of current titles. But as soon as people ask about the cost of buying a book their jaw drops to the floor. Many people simply do not want to nearly the same price for an ebook as they would for a printed copy. Especially since they would have to invest $100 in an ereader. I'm also guessing that people attach value to physical objects that they wouldn't attach to computer files.

The only thing that sales tell publishers is whether their product is moving or not. Ideally that comes from market research rather than anecdotal evidence, but anecdotal evidence will have to do for people like us (since publishers are unlikely to publish the results of their own research).