TERRY - I suspect an accident like you posted happened long before 2004 to cause the OEM's to include safety switches on tractors back in 1980.
Those accidents are tragic, but common sense would prevent them. I've been around rotary mowers since I was very young, from little 7 HP CC's to Bush Hogs run by 50-100 HP ag tractors. When a bush hog hits something it's like a bomb going off under the mower. IH even made/sold ballistic shields for their tractors from solid steel to protect the operators from flying debris. The operator on a CC has much more protection since he's over the mower, but still can be struck by debris bouncing off fences & walls. Rocks, sticks, debris can fly 20 ft or more with considerable force from a CC deck. NOBODY should be around a rotary mower when someone's mowing. When SON & I both used to mow We seldom if ever ran on the discharge side of each other's deck. Just isn't wise to tempt fate that a stick or rock could be ejected.
I've been employed at a couple companies who suffered thru liability lawsuits. The accidents are tragic, the punitive actions against the OEM won't bring the victim back or cure his pain, but they all have one thing in common, somebody was in a hurry and did something pretty stupid.
My personal opinion is that no amount of safety switches or interlocks can take the place of a safety-conscious operator of any piece of equipment. I'm also very aware from personal experience that "Stuff happens" most times very quickly when mechanized equipment is involved.
My Cubbies all have the clutch/brake pedal safety switchs, as do my pickup and work car, but My FARMALL's don't and never did have them. But the lessons I learned fifty years ago running them is still how I operate everything I own now. Check oil & gas before starting, always put the trans/PTO/etc in neutral and depress clutch before starting, and always look before backing up.
I do have to agree with Matt & Wayne. When my equipment is at shows or in public areas I have the key in my pocket. When I let someone else run my equipment I give them a brief rundown of "Special Instructions" for proper & safe operation and I don't allow just anyone to hop on and go for a ride, same way I treat everyone else's equipment. I also watch the person running my equipment for a few minutes to make sure they run it in a safe manner.