That's true, but I still feel like the nature of MMOs encourage the "novelty factor", even if it's longer than many video games. Chess, Go, Starcraft, Sim City and other timeless games share the characteristic of being different and continually challenging. Most MMOs have a tendency to get repetitive. Sure, you can go on raids, trade, etc, but there's not the continually evolving strategy and new challenge of a different style of play, new sequences, etc. The games engine simply isn't that rich, it's underlying structure is still limited.