I wouldn't let my 4 year old ride this ride, regardless of his height. I don't think at that age they can understand that it is pretend and not reality. Nevermind the fact that they would easily look away from the screen and then get sick. Who wants to have this ruin a day at the World!
I think it's awful what happened to that little boy, but as others have mentioned, it must have been in connection with a medical condition that they didn't know about.
We always go on questionable rides first and then decide whether our child would be able to handle it, regardless of what the height requirement says. The height requirements are only there for safety reasons, they can't dictate whether it is appropriate for a child's maturity level.
I think it will be a few years before my son graduates to MS, he needs to go through the natural progression of rides first to build up to something like that.
Nancy
Nancy