You summed it up Chan in your last sentence. It has nothing to do in the real world w/ your exposure. Like others said, everything has to change together. With film, it's usually an indicator for what the film's grain will likely be like, as low ISO films tend to be more fine grained than high ISO films, but it escapes me as to how that would influence exposures. I'm not sure why it would be different over there in the D forum, but as I only shoot film I'll leave that one for others.
Makes absolutely no difference whether you shoot film or digital, it has everything to do with your and my world if you are actually taking pictures.