LAZ--
[Edit-- upon reading the below, I fear the comedic nature of my reply is not readily apparent enough for all audiences. Please don't take the "academic throwdown" tone seriously. I kid.]
* Analogy is a useful tool for hypothesis, but it doesn't cook pigs. You can test your implied hypothesis by roasting skin on and skin off hogs under identical conditions.
*I didn't make a generalization about pork, I spoke of a whole hog.
* I spoke from observation, not hypothesis. Feel free to discount my veracity. As you know by now, I do tend to make crap up.
* To attempt an answer to your (perhaps rhetorical) question, my pigs tend to weigh 120-150 lbs. and a chicken weighs maybe 4 lbs. There are some basic physical differences in surface-area-to-meat ratios that seem self evident. Maybe near the surface you'd see a difference, but when one is cooking a pig for 8-12 hrs, you don't have much "basting" or smoke far past the first few centimeters.
* It seems that pig fat runs throughout the meat in a way that chicken fat does not, allowing internal "basting" which is more important.
* I thought basting was a myth debunked by Cooks Illustrated anyway.
* All that said, I tend to roast hogs in a closed system -- i.e., lid down. Everything stays pretty moist. The charmingly inefficient and risky method of spit roasting over an open flame very well might call for more attention to lost moisture, and the skin might well help retain the juices. In any event, skin tastes good and should be part of the final blend, so I'd leave it on.