If you look at what happened... The original offering was in PDF and HTML format. To me, this indicated that the folks at TOR thought that people were going to read on their computers or print to paper. Later offerings came in MobiPocket format, and I believe that was because so many people wrote asking for a true eBook format.
It appeared that TOR chose first books of series to motivate people to buy the subsequent books -- which they thought would be the paper version of the book. It was the clamor for MobiPocket (and Sony) formats that I think has finally convinced them that there is
- A market for electronic books
- A potential for lost sales with eBook reader owners refusing to buy paper books