My wife and I have been discussing this heavily since it happened, as we're pretty big fans of the parks and have lived 30 minutes from Florida our entire lives, basically sharing the ecosystem and prevalence of gators. They're everywhere, but that's usually not a problem. In fact, a water moccasin is WAAAY more cause for concern than any gator. When she told me what happened, I was like "Dear God.." but none of it didn't make sense.
Disney has this artful approach to constructing facades that has finally culminated into a tragic freak accident. They're known for taking this swamp and turning into whatever they want it to be, but that doesn't fully eliminate the swamp. So you have these beaches made right up to a freshwater lake teeming with far more than just gators. Combine this facade with the (acceptable) ignorance of someone not from that area, the time of day, the size of the child, and the level the child is submerged, you get this one in a million scenario that just sucks. Blame (on either side) doesn't even begin to cover this event, it's too multifaceted for that.
But this does probably serve as an eye-opener for Disney, who is so committed to this ultimate dedication to constructing fantasy environments from very real ecosystems that proved so effective that it leads to a tourist probably thinking his son was perfectly safe. Combine that with their dedication to subtlety in obligations for safety (a simple, non-threatening "no swimming" sign instead of a more valuable and explicit sign that "ruins the magic"). It's certainly worth thinking about.