The grind though provides a reason to do more than just that, since after a while it can get old without something else driving you to play. A lot of folks though don't even notice the grind in games when they play with friends. I can't begin to count all the times I leveled in vanilla MS without ever paying attention to the exp bar rise just because I had my friends to talk to and sit down and recover MP with (and this was back when you were getting like .02 -.03 exp per kill at level 30.) It wasn't the grind itself that made the games more fun, it just created a situation where you'd be playing the game for a long time and want to talk to people to help kill the time.
But the grind also made it so that things such as builds and getting certain gear were way more important because you used them a lot longer.