True, both can briskly past a journey of hours, days, or weeks in mere minutes, and conversations between characters (player or NPC) can move as briskly as conversations, but let there be an attack on the way, and the RPG explodes into a session-filling encounter. Or possibly more than one session. While the book will be done with it in as little time, and probably less, than it would take in real life.
A book you can read in a golden afternoon will fill many, many, many sessions of a RPG.
There's also the effect on leveling up. Legends and fairy tales are no help there. A hero can slay a giant or a dragon at the beginning of his tale or, if he can't, will briskly solve the problem by being nice to the old woman on the way, or robbing a wicked witch's house, or something, and thus walking off with the magical object or three he needs to do the trick, or perhaps even the allies who will do it for him. No leveling up required -- the hero saves the kingdom as his first trick.
The only analogy that exists to leveling up is real life, where there is no substitute for grinding practice. To reach 11th level where you are marked out among adventurers as special would take years of practice, probably from a young age -- which would take decades of gaming. You can fudge up plot devices to explain why a band of four to six heroes can become world-shaking powers in what amounts to a year or two of story time (barring such contingencies as forcing them to spend travel time between chances, and varying somewhat based on the experience required), but their purpose is a little visible.