Well, pornographic parodies/satires on super heroes are old. What makes this one differant is that they were actually able to use the Batman characters as opposed to analogies to them. Given the copyrights mentioned it seems that DC Comics is fully in support of this project for whatever reason.
That said, someone already mentioned "Orgazmo" (which was not a porn movie, despite the plot) and of course you had things like "Penthouse Comix" and characters like "Night Girl" (for straight porn)... but that isn't the same thing.
I suppose this shouldn't surprise me terribly given the existance of mature/adult comics labels being run by the major comics studios. DC has both Wildstorm and Vertigo. While not straight porn "The Authority" has analogies to Batman and Superman as a gay couple.
This is not to say anything about all of the fetish costumes (especially batman and batgirl inspired) sold for big bucks to the kinky by leatherworkers.
Ah well, all rambling aside I think this one is making history to be honest, and truthfully it shouldn't surprise me as much as it did at first, because as I've been rambling about, the industry has been moving in this direction for a while.
Makes me wonder what Marvel is going to liscence out for a porno in response.... I'd be very surprised if it doesn't happen.