The difference between a 69 and a 70 is 6 to 10 times the value? I'm new but I don't get it!

I just don't see how a coin that is 1 point higher on a 70 point scale can be 6 to 10 times more valueable than the one just 1 point less in grading. Is this a bubble that will burst or is this a come on by the slabbing companies to generate business. I have looked at over 75 coins graded 69 and 70 and can't see a difference. Whats up?