I think tht what makes JP different then other drop rides is that the fall is in the dark. As you approach the fall, you kinda don't know what your in store for. There's no view of the landscape and uncoming fall to prepare your self with.
I remember riding the Tidal Wave log ride at Busch Gardens, which is 55 feet, before I was even brave enough to try coasters, and not having any problem with it. Of the couple of times I have riden Splash Mountain, I have never been truly scared. I think, with both those examples, the easy part comes when you reach the top, and you can assure yourself by assesing how high you are and route the boat will follow. It's as easy, for me atleast, as reaching the top of the coaster mountain, and realizing how well strapped in you are, and where the track is headed. (Most people are scared of coasters because they choose to close their eyes during thr ride, and imagine the most horrible things).
With JP, there isn't that view. You're kinda just falling into darkness. While on the other rides you can look up at the sceanery, or down towards where your going to fall, on JP all you can do is brace yourself and stare into the dark. The hight of JP has never been a factor for me; It's the uncertainty of the whole situation that gets to me. The same goes with Ripsaw. While Ripsaw does fall in the open air, the unrestraint log seating, plus the change in degree of the fall (from 45 to 50), which gives you the sensation of the log tumbling over, adds to that same uncertenty.
-Kevin