love the use of "solid" when both numbers (50, and the other 50) are pure unobtanium pulled out of an orifice.

"a lot" would be less rhetorically satisfying, but probably more appropriate.

I suspect the number is in fact, far less than 50%. In mining engineering, I'd be amazed if a significant majority of the rules don't stem from a significant accident or death, or forseeable need to avoid them. In medicine, the stakes are equally high. Building codes? It depends. The cost of tunnelling in NY isn't because of government compliance.