That isn't entirely true and brings up an important nuance. I understood algebra and calculus extremely well but I routinely got half-score for fudging a calculation or somesuch because multiplication has a foundation of rote knowledge: you need to memorize you ten-times table. To this day (at 37) I continue to use algebra to do basic multiplication in my head (7*6 = 7*5+7 = 7/2*10+7 = 35+7 = 42).
Sure, using a graphing calculators solve the problem isn't demonstrating understanding, but 90s kids were simply asking for the basic calculator with 2 registers (display and M) and basic math and "sci" (sin, cos, sqrt, etc.) operators.
Preventing use of basic calculators does nothing to demonstrate knowledge of math at all, it actually hinders it.