They more did it for a simple cluster layout plus some cost cutting. Blue light means engine coolant temp is below 50 degrees celcius. Peak operating temp is around 85c, though it can go up to 110 and still be considered normal. Once it gets too hot, you'll get a red coolant light and if it's dangerously hot, it'll flash. In 100% of driving situations with a fully operational cooling system, you'll never see the red light, absolutely never. I heard it comes on at 130 degrees. When I was driving in the mountains in around 100F, I was towing 3,200lbs full throttle with A/C on for about 5 full minutes. My coolant temp never exceeded 105 degrees. In my Volkswagen, I have a proper gauge but it's tuned so that it will stay in the middle(90c) all the time. It has a threshold of when the car is between 70c and 120c, it'll read "90". So it's no more accurate than a light.