The case in Vail was he was skiing to fast to be able to stop safely to avoid obstacles, such as a person. As a new school skier, I would say the responsibility is on the 'victim' on the landing, but legally I would say it might fall into the hands of the jumper. There are always signs saying 'have someone spotting you jump' 'check the jump first'. Whether these would hold up in court to be able to be used against you, I dont know.
Prevention starts with education, I was on a CSIA course and the level 3 instructor stops us (a group of 12) on the landing of a jump not visible from above in the Whistler park. Unbelievable. No one said anything. Its ridiculous. A park is a dangerous place. Blackcomb has now gone the route of other big parks and fenced in thier big park, a smart move that keeps people who dont know better out, and the landings clear.