Okay, read all of this stuff — including the Suspiciously Awesome paka's comment — before continuing.
The campaign that I mentioned is the first time I've ever played an variation of a table-top RPG, makzu's experiment aside. (Sorry, Makzu, that was more Internet-top. (Mmmmm: the Internet as a top. Sounds like a l337 time.)) Even with such a short time playing, I can see a few patterns emerging. I'm willing to bet that every system has some Golden Red Herring built into it, and that inherent flaw tests the personalities of the players.
Shatterstripes (AKA Peggy, Patron Lady of Vector Art that is BETTER THAN YOURS) mentions that many players chase those points down: loot, levels, experience, ability scores, and gold points. The system is built for it, she argues, noting that most of the source-books were devoted to those points and not storytelling of characters. I think she's right, and I'm even going to expand on it: every RPG system has these little prizes in it. D&D has loot and levels, with the rewards of character power. Mutants and Masterminds has instead experience-like Power Points, with which we directly make our characters stronger. Rifts is... Rifts. All these games have the open and obvious built-in temptress of Munchkining. That's why the card game Munchkin is amusing: it is the distillation of the entire issue. (It might also be a round-about way of attempting to solve it, and I wouldn't put it past those sneaky bastards!)
You can't win these games. There's nothing at the end of that tunnel of experience. The games do not get any more fun with increasingly larger numbers. I suppose there are things characters can do with all that stuff that is like winning: building an empire, becoming a god, or just really upsetting the game universe. Those have a very limited appeal, though: there's gods, empires, and roaming disasters enough. Besides, there's always a bigger fish out there. Thus, a good player attempts to do something different. What's something? Everything.
So, players face a choice when they pick up some dice. They could chase those Golden Red Herring, or they can open themselves to the possibilities. Maybe they can let the GM tell them a story in which they get to engage. Maybe they can explore a whole new world, or play and interact with interesting people that are not possible in our universe. It's a great big multiverse out there, and you have the d20.
Now roll initiative.