I read the game of thrones novels ages ago in pulp paperback and tried to read the fifth one as an ebook and I simply could not keep track of the various character story lines, names, etc. that I had no problem with while reading the physical books.

I'm very sure that just remembering how much of the book was in my left hand and how much in the right was extremely valuable in helping me remember - basically having an additional dimension recorded in my memory made it much easier.