Markov chains help a lot in making the output look like the real stuff, that's kinda their purpose in this case. Heck, there have been automatically-generated conference papers that have been accepted and went through peer review (although this might tell a lot about that process, too ...).
git manpages are apparently full of very git-specific terminology and quite dense. I would guess the same model applied to the J documentation would be equally unreadable for the uninitiated. If the source material was more readable and easier to grasp the automatically-generated versions would reflect that (to some degree, until it's obvious that's nonsense).
The generator doesn't use markov chains, it's grammar-based similar to the Dada Engine which powers the postmodernism generator. There's a link to a markov chain based generator in the footer, check it out, it's pretty funny and a lot more random.
I stand corrected on that point, then. But still, I guess it's no surprise that something tailored to look/sound like something else looks/sounds like that something else ;-)
