I was talking to an upper management at CP once while I was an employee and I asked about the height requirements like that, and they agreed that it is also the maturity of the rider that's a concern. Not so much can they handle the ride (more afraid of them freaking out and being too scared) but how mature will they be in a 2-3 hour wait without annoying the rest of the line! Of course, it's not a perfect system.
The height part is not set in stone, because for individuals that are below the height requirement but are adults with not physical restrictions, you can get a special pass at CP (similar to the handicapped passes) that shows you can ride anything, regardless of the height requirement (no special access, just you don't have to argue about it with the entrance host). Mantis might pose a problem, of course, but the rest of the coasters aren't a problem.
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/index.html