Some years back a former Kodak guy, Dick Dickerson, had an interesting article in Photo Technique [sp] magazine, where he simulated "grain" using an Excel spreadsheet. (Try making two columns with a random function, =RAND(), then show results on an x-y graph.) The result was shown on a 2D graph, and had a striking resemblance to "grain" patterns. (Hit the recalc button to see different patterns.) So it seems likely, or at least plausible, that what we see as film grain can be largely explained statistically as a somewhat random distribution. Real film is not limited to a single plane, so grain patterns can be much more complicated. A second comment relates to what we see as "grain" through a microscope. Years back, circa 1980(?) I had set up some QC procedures to verify "adequate" preset focus on a proprietary camera system. Essentially, resolution targets were photographed, and the processed film was rated via a microscope - somewhere around 50 to 100 X as I recall. I still recall initially seeing the "grain" (actually it was color neg film) and thinking that it would limit the resolved detail. Then being surprised to see that the resolved detail was much finer than what seemed possible. I won't try to explain except to say that anyone looking at color film "grain" under a microscope without an underlying "image" may be easily fooled as to the limiting effect on recorded detail. After this, I looked at grain as not setting a limit to fine detail, but being more akin to a coarser overlay that could obscure some of the underlying fine detail. Ps, if it matters, the film used was the Kodak professional color neg of the day, either VPSII or III.