As of June 2006 there had been 15 deaths at WDW since 1989 and none of those were officially blamed on Disney, altho two of those were CM's and they were questioned at the time
(Source)
About 10 years ago I came across a document that was a WestLaw search of injury and death lawsuits against Disney. Almost all of them were won by Disney.
In a few instances Disney was partially blamed for things like slow response to the emergency.. apparently this happened with a child who put their hand in the water at Pirates and lost a thumb when the boat bumped a metal guide in the water.
Deaths at DL are better documented online for some reason. Basically there were a few people who did very questionable things and paid with their lives. Standing up or trying to wiggle out of the restraint devices on roller coasters for example.
At DL, one castmember was crushed by the America Sings (formerly Carousel of Progress) attraction when the theatre rotated and she was caught between two walls, one moving and one stationary.
At WDW, an employee was killed prior to park opening, when the Skyway started up while the CM was cleaning the loading deck and he was scooped up for a period before falling some distance.
And at DL there was the Columbia ship accident where a guest was killed when a large metal thing that the boat was tied to broke free and hit the guest and his wife.
Most of the injuries or deaths at Disney can be attributed to : (in order)
1) Pre-existing health conditions : Heart problems or other undiagnosed conditions in children and adults alike can cause problems. And they do.
2) Guests Who Defeat Safety Mechanisms: Guests who do things they are advised NOT to do, sometimes get injured in the process.
3) VERY rarely.. something goes wrong. This happened once when a Big Thunder car separated from the rest of the train.. that kind of thing. This kind of operational failure is extremely rare.
While any death or injury is to be avoided, still, assuming an average of 10 to 12 million guests a year at MK alone from 1989 to 2006.. that's 204,000,000 guests.. and only 15 deaths.
That works out to a 0.0000000735294 % chance of death from any of the above causes while at WDW.
That's an enviable safety record by any standard.
Knox