People's physical conditions and traits vary widely. These mainstream attractions are mainly designed for the average fit of a person, in order to serve the largest amount of people, with accommodations made for the variables.
Every seat cannot be made to fit everybody, since there are so many different types of people in the world. Some people are too short or too tall, have a handicap, or are too big. These are all physical traits, non of them more pertinent or deserving then the other.
A person that is too big to fit in a regular seat can at least try to sit in the special seats. If they are too big for those, or feel uncomfortable in them, then it's too bad. They can't ride. If you feel that every attraction should accommodate big people perfectly, then shouldn't they all also accommodate the short, the tall, those with handicaps, pregnant women, those with heart conditions, ect?
Or better yet, what about those people who are too big to even get out of bed? Should every coaster seat be designed to accommodate them some how? Some may say this example is far too extreme, but it just shows the absurdity of wanting everything to be perfect and fair for everyone all the time.
You said it wasn't fair that all the big chairs are in the 3rd and 6th rows, because you don't get to ride the front row. But, when Ms Dis mentioned that MIB9 was uncomfortable in the Rockin' Roller Coaster seats because there was not enough room for his legs, you said that he should sit in the front, where there's plenty of room. Well, what if he doesnt want to sit in the front? By your standards, every seat in the RnR coaster should be adjusted to fit MIB9's lanky legs.
I'm a small guy. I'm 5 foot 5 inches at 20 years old. I had to endure not being able to ride some attractions longer then most people. This is a physical trait of mine, something that I can't help. Was it fair that younger kids got to ride coasters before I was able to? No. But lifes not fair.
It's good that they at least try to make an effort to include as many types of people as possible, but you can't please everybody all the time.
-Kevin
P.S. While I love roller coasters, the water plunge rides, like JP, still manage to some what freak me out. I only feel truly comfortable when the lap bar is securely on my lap, holding me in place. But, whenever I happen to be on JP in the same row as a large person, the lap bar lowers onto them nicely, but hovers a good couple of inches over my lap. This makes my seat uncomfortable, but I also know there's nothing that can be done about. It's just the way the cookie crumbles.