"The results are…
"The results are oversimplified for consumers using a “Five-Star” safety ratings system."
IIHS rates vehicles on a four degree system, "Good", "Acceptable", "Marginal", or "Poor." By your logic, isn't using four degrees instead of five an "over-oversimplification"?
That so many vehicles today receive four- and five-star ratings from the NHTSA is itself proof of the agency's effectiveness - manufacturers are motivated by sales, sales are contingent on consumer perception of the product offered. Who would want to buy a two-star car? Vehicles are built to higher and higher safety standards with each passing year, and when tested they score higher than their predecessors. All of this is a good thing, unless you actually are arguing for a "diversity of safety," where manufacturers are somehow encouraged to expand their product lines and build less safe vehicles only to have a wider spread of crash test scores...?