Height requirements having everything to do with how a coaster's designed to be ridden. Frankly, the big ones aren't designed for the sub 54" crowd. The seats, restraints, and elements of the coaster all work together in the design. The designer's not visualizing a young child being put through the forces of his scream machine, he's visualizing an adult. Ergo - a height requirement AND one that shouldn't be messed with by parents who can't bear to say 'maybe next time' to their eager youngster. They have their whole life ahead of them, why on earth would anyone play games with a height requirement out of fear of some tears over not being able to ride. You wouldn't put them on a dirt bike early, don't put them on a roller coaster early.
And, for the record, each new coaster DOES use dummies, specifically water dummies to simulate riders before the new coaster opens. Unfortunately, in Tatsu's case, they started leaking.
Water dummies are great because of how easy the weight shifts and how accurately they simulate people, since people are 'large bags of mostly water'.
-- PMM
