Interesting if the 48" requirement is the rule for riding alone. I say that because at none of the rides that my son rode alone (either as single rider or while I waited) was his height measured. He is almost 5 ft tall, but I don't recall any way for the ride attendants to have measured him (or any other child) for that requirement prior to getting on the ride. We specifically asked the employees at the entrance of Gringott's if he was old enough to ride alone before we got in the single rider line, and the two people working at the main entrance did not even know what the single rider requirements are. They had to go find someone else to ask (who basically just said yes without measuring my son or even asking him his age).
Overall, Universal seems to be quite different from Disney in this regard. Of the rides we rode that had a height restriction, I only remember seeing a measuring stick at the very entrance, and the ride attendants didn't seem to be really strict about checking (maybe this was our experience because my son was obviously tall enough to ride?). I know at Disney, quite a few of the rides with height restrictions have measuring sticks/CMs at multiple points along the queue to check and re-check the height of shorter riders, and the CMs are very strict about checking. I did not observe this to be the case at Universal (although, we did not ride any of the "big" coasters like Hulk or Rocket).