My aunt pointed out that for her, John Lennon and Jimi Hendrix were ones that hit her hard, because their music is such a part of her life. Their death is a part of our own history dying as well. The Seattle sound was such a part of my youth, yet as of now almost all the major Seattle icons have died, all before 60 and some before 30. Obviously the most famous and iconic was Kurt Cobain's suicide in 1994, but that was predated by Andrew Wood who died of an overdose in 1990. Since then Layne Staley and Scott Weiland have both passed on as well. However, with both of them it was drugs and, while very sad, wasn't exactly a surprise. Scott Weiland's death in particular hit me, but again, not shocking.
Cornell, besides being the most versatile musician of the lot, was also the one that had beaten drugs and booze, was still a prolific songwriter and was very healthy, physically at least. He was still making decent music, and unlike so many other classic rock musicians who release new material at age 50, his was still really good. I think it was such a surprise and shock because it was so senseless.