The point is that I do not think immersion (or whatever term you like) is what it claims to be, or what people claim of it. Here I'm with Fang: I don't think people immerse in quite the way they imagine themselves to do, at least not generally. The interesting thing is precisely the disjuncture between that they say and what they do.
In other words, if "being" the character in whatever sense is valuable or interesting, it is so precisely because one is not the character. It is the fact that immersion does not occur radically that generates power and tension. And this is quite normal: it's how quite a lot of ritual behaviors work. There is a kind of meditation on the difference between what is idealized as "supposed to happen" and what has in fact actually happened that helps prop up the ideals themselves. That's simplistic, but accurate enough in its way. (There are of course ritual processes that are utterly immersive in a strong sense, but many of these use physiological techniques to assist: sleep deprivation, drugs, physical punishment, etc.) So I do think that something nebulously like "immersion" is embedded in the ideology of the SIS.
Actually a great deal of Chris's writings circa 2005, when he was engaged in criticizing RPG theory via anthropological concepts of ritual and "bricolage" is worth revisting from time to time. (Note that until mid-December 2005, he was posting his RPG musings in his personal blog--here's a useful link.)
What I'd suggest is new, reading Chris and Zak together, is that unlike our rational attempts to hierarchically circumscribe fiction as a bubble, membranously separated from reality (cf. Tolkien's "Sub-Creation"), the process of bricolage is "flat" and continuous. Zak illustrates that the membrane is semi-permeable, and really, that's a positive feature.
Although I hasten to add that theories of gaming which then try to fixate or reify the social processes of gaming, in the name of transparency or empowerment, have their own problems. Why? First, because they frankly throw the baby out with the bathwater--if they succeed, then the actual social process is stunted. But in fact, they can't succeed, because the social element is always there. You either have a functioning social dynamic, or if you've got a group that's prone to power struggle, then the mechanics themselves just become a tool for crypto-struggles, starting with fighting over what game to play in the first place.
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Another quote by Chris, that buttresses what I'm talking about (which in turn is largely an interpretation of other things he's written):
RPGs are interesting (but hardly unique) in part because the players so often do insist (and experience as true) that larger social structures of their society do not enter gaming, when in fact this is quite obviously not the case from an exterior perspective. This process of claiming an absolute barrier in this way is a part of what Cathy Bell means by "ritualization," except that I think most traditional religious cultures (please let that horrible phrase stand; you know what I mean, I suspect) do not go so far as to say that there is no connection between ritual space/time and other spaces and times. That I find unusual (but not quite unique), and it is in any event a very strong ideological claim.