The Fiction Becomes the System for Advancement; Or, Something Needs to be Heavy

In the comments on a recent entry, the subject of rules-lite games and level advancement came up. It has always been my position that problems with rules-lite games arise when they become so rules-lite that they lack sufficient 'crunch' to be used in for a long-term, open-ended campaign. A long-term campaign needs advancement to give impetus to proceedings, and this is harder to achieve in direct proportion to how ephemeral the rules feel. The good thing about advancement in D&D, for instance, is that by going up in levels new possibilities are opened by virtue of the fact that the system incorporates many options and add-ons - there are new spells to learn, new magic items to find, new abilities to develop (depending on one's edition of choice). This is harder to achieve with a rules-lite system where all one really gets to do is fiddle around with a very limited number of stats or abilities. 

However, I am persuaded, as commenter diessa puts it in the post in question, there is a case to be made that one can - if only one is of a mind to - run a rules-lite campaign in which 'the fiction becomes the system for advancement'. The idea here is that the PCs have goals that are intrinsic to the 'fiction' itself rather than extrinsic ones to do with improving stats, hit points or whatever - solving murders, say, or social advancement, or earning lots of money, or realising some project or objective. And here it wouldn't matter that the rules are 'lite', so to speak, because they would only exist in order to provide a basic framework in which 'the fiction' can evolve.

I can buy this to a certain extent, but I think it misses something important, which is that in order to get to a point at which 'the fiction becomes the system for advancement', there still needs to be part of the campaign that is heavy in the sense of requiring lots of careful thought and probably a great deal of procedural moving parts (but which might be hidden from the players themselves). For instance, I can easily imagine a long-running campaign with a rules-lite system being successful if it chiefly involved investigation - a crime procedural, for instance, or an Unknown Armies or Call of Cthulhu-style paranormal mystery. But I can't really imagine either of those things working without the DM having to invest a lot of time in figuring out ways to systematise the distribution of clues, connections between NPCs, random events, flowcharts dictating what happens if the PCs do X and then Z rather than Y, and so on and so forth; there will still have to be weight, in this sense, but placed behind the scenes rather than being foregrounded in the player-facing rules.

Similarly, I can imagine a long-running campaign with a rules-lite system working if the PCs were, let's say, merchants or traders or businessmen or whatever. But, again, I can't really imagine it working without considerable weight being placed within the commercial or financial aspects of the game - without, say, a way of figuring out what is profitable, in what context, and where. 

In short, the argument that I think I am making is that in order for a long-running, open-ended campaign to be a success there is a requirement, even in the context of the rules as such being 'lite', for there to be an aspect of play which is heavy. There has to be something that has sufficient heft to bear the load of sufficient interest and intrigue in order to keep the campaign above water. I am not convinced that it is possible to sustain long-term gaming with mere 'fictional advancement' alone.