There are a lot of flat rides and some coasters that have 48" as a requirement. Where I work the majority of rides have height restrictions of 48 inches or less. As for the parents waiting with their too small children and being rejected, there is a sign at the entrance of the line with the height requirement, and a nice little arrow showing how tall a person has to be to ride it, so if they waste their time it is their own fault. I know it is a hassle I have turned down many kids on the "taller" rides. The parks never state that with the adult ticket, one can ride every ride and coaster in the park, but they can usually enjoy the majority of the attractions.