Why offer free digital books? Well, mostly because it gives me a chance to get folks reading. The fact that I get to inflict my sense of humor upon the unwilling masses is purely a side benefit.
While I've no problem reading stuff on-line, some folks just love to kill trees. Oh sure, there's plenty of reasons to provide a print version, including "I get painful eye-strain from staring at a glorified TV", "I don't want to get sand in my Kindle", "I love to make little squirrels cry", but ultimately the reason I like to do it is to make little baby squirrels cry.
Have at, and feel free to let me know how much I suck.