I would suggest that people's relationships with books are much more complex than the casual vs. avid reader categorizations can encompass.

Take a simple example: it seems as though the majority of active members around here are actively engaged with novels and non-specialist non-fiction. Yet how would a reader of technical books fit into that categorization? Are they avid because of how much they read? Are they casual because their reading may be geared towards professional development? How would people who want to read, but don't have the time (or interest to devote much time) to read much? They may have a to-read list, much like us, but they may not pursue it to the degree we do. Those books they want to read may be popular titles, bet things that they didn't have a chance to read years back, or may be books that they want to re-read.

The reasons for reading are probably even more varied than the reasons why those people aren't reading. Just because someone doesn't dedicate the time to reading doesn't mean that they aren't interested in genre titles (new or backlist), classics, etc.. I think it's a shame to say that these people want to read something just because it has received a lot of press or because they're stuck in an airport. That's almost like denying that they are people who have similar interests to us, but may seek to pursue those interests in different ways.