Why do firemen rescue acrobats from trees?

Eons ago there was an old bit on SNL in which a Ghandi-esque guru pondered the great questions of the universe. "Why do tornadoes always touch down in trailer parks?" he asked. And"Why do firemen rescue cats from trees? Cats are natural born climbers. How many cat skeletons have you seen in trees?" To the list, I'd like to add "Why does the GSView PostScript viewer launch much, much, much faster than the PDF viewer brought to us by the creators of PostScript?"