Yeah, I guess part of the reason we tend to find the here's-40-pages-about-harpoons sections tiresome is because if we, in 2013, want to learn about what it was like aboard 19th century whaling vessels, we have options. Google, maritime museums, college courses, the Discovery Channel. But when that book was written, the only way to know what it's like on a whaling ship was to go be on a whaling ship. Or maybe you'd run into some crazy-ass dude who'd been on one and is willing to tell you all about it. Or if you're lucky (and literate), you'd come across a book about it. Living in the information age allows us to know how big the world is, so to speak. But some barefoot doofus living in Wyoming in 1851, not so much. To him, 40 pages about harpoons might've seemed kick-ass. Hey, it beats staring at the wall. Or syphilis.
There's a cool scene in Django Unchained in which Jamie Foxx asks Christoph Waltz to tell him the German fable of Broomhilda. Foxx's character sits like a little kid, in rapt attention, mesmerized by the faraway tale. The scene captures how information-deprived a person could be in days of yore. If someone had a story you hadn't heard, or wanted to give you an lengthy treatise on harpoons, you'd lap it up. It's not like you had a spin class you'd be late for.