I wanted the folks at Logos to know that many of my recent purchases were motivated largely by knowing I could read these resources on my iPad. Without having access to at least the reading, highlighting, and note-taking ability this app gives me I probably would not have spent the money.
So if Logos wonders if their mobile apps generate any revenue, may I say that from my experience that they do. They are not just another way to use what I already own. They help motivate me to make the decision to buy.