Some books being on that list I can understand, either because I know they're heavy stuff, or because people might find them badly written or boring.
On the one hand I'm surprised to see LotR on that list: it's not a boring book (to me, at least), it's very well written, and it's an easy read (for me). On the other hand, it IS a novel 1200 pages long, and I can understand that people who are not "trained" for that, are not ready for such a long story.
And, you've got the people who are not into reading fantasy and still try to read LotR because they "should read it", or because they saw the movies and thought to just have a go at the book. These people will invariably fail to finish it.
I keep re-re-re-re-re-reading it, including the appendices. (So, sue me
)