I assumed that Ron meant something like, "following the carrot of reward [in whatever game he was talking about; i forget] does not actually incentivize exploring the game further."
In Chronica Feudalis (a historical-medieval adventure game that stole Aspects from the FATE system), there are only two sources of currency or character improvement. One of them involves Aspects: if you let your character's Aspects be turned against him/her, you get a reward which can only be spent to activate OTHER Aspects, yours or that of the scene (like weather and stuff) or that of other characters.
So, it's basically a zero-sum game for the players: every time they let themselves be kicked around a bit, they can do the exact same thing to someone else. It's all very GM-led (the GM has infinite Aspect tokens), and this isn't to say it's not fun, but you don't really change or develop from this - you're just poking and prodding at what's in front of you. Pure Exploration of character and situation, no inherent moral or ethical dimension at all (so no "native" support for Narrativism), and honestly the fact that the GM has infinite Aspect-tokens (or whatever they're called) means that there's no way in hell this game is "battle-tested" as a good supporter for Gamist play, as GM/player competition is hopelessly one-sided -- the GM can spam your Aspect: Self-Defeating til the cows come home.
So - second reward system: skill training. This one is actually a very different sort of Simulationist logic - - while Aspects are actually a pretty neat way to chew the scenery and Explore being a medieval person, skill training relies on the logic of "game-system-as-physics" - that is, the idea that the rules must accurately reflect the way cognitive, physical, and institutional processes *actually function* inside the game-world.
Going off to a trainer does fuck-all to add to your Exploration of being a medieval person other than to give you ... Exploration of what it's like to go to school as a medieval person. Given that there is very little focus as to what one "does" in Chronica Feudalis, I suppose a game that centered around training facilities, or at least featured them meaningfully, could play to the game's apparent natural points of focus. But this is meeting a good-but-uninformed design a good deal more than halfway :)
[EDIT: my bad! Turns out I had only read the advancement rules about halfway through. Here's how it works:
1- you train with a mentor or by yourself, turning one of your skills into an "in-training" skill.
2- you go out and use that skill in a scene "where something is at stake" (quoth the rules)
3- either make a skill check for that skill, or make a skill check of your trainer's skill - - ChronFeud skills use a die-step system, so your skill's rating is in the form of a d-whatever. Thus, improving a d6-rated Swordsmanship skill would require a 6 or higher on whatever skill check you use, so training with a.. trainer who is better than you would make more sense than training alone, especially when you get to higher levels of ability.
4- once you successfully improve a skill thus, it is no longer "in training" until you do this all over again
I admit, that actually makes some good sense, from the perspective of a Sim-style "game-rules-as-game-physics" approach.]
At this moment, it seems that I have a much better idea of what Reward Systems are: they are the system's internal structures that encourage you to play the game a certain way (design intent made manifest). If you want to play the game a different way, it usually goes one of two ways:
1- the game fights you, actively hampering your ability to play the game you were "hoping for". Such games cannot be Drifted without extensive reworking of existing rules. White Wolf games come to mind; I'm no fan of the Humanity system, the Paradox system, any of it, because it doesn't do what it's trying to do in a way that actually helps me explore the themes I see lying dormant in that content. Sorcerer does Humanity better by a country mile than Vampire could ever hope for.
2- the game just lies there, forcing you to bring your Creative Agenda with you in a suitcase, so to speak - that is, the rules are open or sparse enough (in terms of what CA you were hoping to engage in) that you can work entirely on the level of the fiction to make things happen. That is, in the case of ChronFeud and Narrativism, if you write up a few leading questions for PC creation in order to tease out a Kicker or two and some intra-party juiciness, you can use these answers (much as Apocalypse World does) to "kick off" play in the right direction for what you want. AW, however, does it a fair sight better in that it combines the leading questions with a LOT of tools for the MC to keep things moving. Without those tools (present in the system or present in the group's skillset), there may be a fair bit of difficulty keeping things going once the initial "steam" of those Leading Questions runs out.
[EDIT: despite my corrections above, I stand by this second point, here. The only thing that the training system adds to the game is a sense of explicit, in-fiction cause and effect for improving your character's abilities. Many, many other games get by just fine without approaching char-improvement in this way, even games that are "fiction-first" like Apocalypse World.
I think a group's time and energy are better spent paying such close attention to the consequences of their actions with regard to the fiction and its internal "logic"; I know that this attitude reflects my own play priorities, though, and if you like this sort of thing, go for it, but I will politely decline any invitation to join in ^__^]