>Do you think that the recent e-book versions have negatively influenced sales of the (Hentzenwerke) books? I haven't heard this reason so far, but your above argument would imply that this has been one of the causes of the drop in sales.

No. Jos and Martin already answered you in more or less the same way I would.
I based my comments on the fact that it is so easy to copy an ebook and unfortunately the professional ethics of many in this world are suspect.

I do not wish to offend anyone but I regularly help in newsgroups where most if not all of the visitors are in developing countries. I have seen many attempts, offers and requests for 'free' software and 'free' books. Call it local economics, or that they are used to a way of life where getting something for free makes them feel good. I call it piracy, a total lack of professional ethics and a shame.