Also the story grew a lot more than Tolkien originally envisaged. I am afraid that I was a lot more interested in Aragorn amd Legolas' adventures when I first read the book and gave up during the long and depressing slog of Frodo and Sam's to Mordor with creepy gollum. It was a year before I went back and finished the book. However there are some very good bits in there - Ithilien, Faramir, Oliphaunts ...... but even so as Eomer rightly points out, there is a lot more going on in the more complex events elsewhere. The hunt for Merry and Pippin is actually only a few chapters but they introduce a lot of new stuff to be sure. They are crucial for the success of the quest though.
If Merry and Pippin hadn't been captured and hunted for there would have been no ents to aid in the defeat of Saruman at Helm's deep and Isengard, no ride of the Rohirrim to stave off defeat at Pelennor, Aragorn would not be in the right place to take advantage of his destiny and ride the paths of the dead - nor would he have the Palantir to challenge Sauron. The success of the Quest depended in no small measure to the eye of Sauron being diverted away from Frodo and Sam. As a result so is the readers!!!
