I, too, feel very sorry for the family. Also horrified at the people blaming the mother and making blanket statements that no 4-year-old should be allowed on the ride. But then, I'm a firm believer that people have to do what works for their own family. My DH, for example, believes that no one could ever get sick on M:S; he finds it very tame and feels the same way about ToT. I was disoriented and felt weird all day after M:S, so I don't ride it any more. I also find ToT terrifying (physically, not theme-wise). My DS is 6 now and has just hit the 44" mark; if he wants to ride it I'll let him. When he was 4...I'm not sure. DS was not very adventurous and would not have wanted to ride it. But my choice about that would not make this family's choices invalid or wrong, just different.
Now, why are we playing the blame game? In a nutshell: sometimes bad things happen randomly, and we all need to assert control over an uncertain world. So if it's someone's fault, that bad thing can never happen to us. If everything scary and unexpected that ever happens is someone's fault, that makes the rest of us safe.
We don't know what happened. Until we have more information, I think it is unwise to say the least for us to cast blame on anyone.