If you're about to remove the riving knife, or making a cut that may twist the wood you should immediately ask yourself if there's a more appropriate tool to use or way to make the cut. If you continue anyways I'd see that as negligence as opposed to a mistake. (To expand on twisting the wood, the longest side of the piece should always be held against something while cutting. So on a rip cut it should be held against the fence. And on a cross or angled cut it should be held against either a crosscutting sled or miter gauge)
Not saying mistakes don't happen. I'm sure there are instances of people doing everything right and still getting injured. But as I explained I don't think it happens often enough and the injuries aren't serious enough to make the risk so unacceptable that we need to add $500 to the price of every new tablesaw.
Wood often has hidden stresses within its structure. An apparently straight length of wood can cup/bow/curl quite markedly when cut. So you can't always know if a particular rip cut will result in the wood binding between the fence and blade leading to kick back.
On the price difference point, I have a portable Dewalt table saw that cost about AUD$1100 with a stand. Saw Stop didn't have a portable version when I purchased. Now that they do have a portable version, it is about AUD$2000, roughly twice the price of similar models from other manufacturers (at least here in Australia). That's quite a price difference for hobbyists and home gamers who aren't deriving an income from the tool.
Not saying mistakes don't happen. I'm sure there are instances of people doing everything right and still getting injured. But as I explained I don't think it happens often enough and the injuries aren't serious enough to make the risk so unacceptable that we need to add $500 to the price of every new tablesaw.