In games, how often is the screen actually making such drastic changes?

Constantly. In first-person-shooter games, such drastic changes are happening over very large areas of the screen practically every frame. And with frame rates being 30-60 FPS minimum, and with a clear and unobstructed view of your target and your surroundings meaning the difference between life and death, an LCD that leaves ghost trails behind every change in the screen picture is not suitable for gaming.

I don't care about things like rise and falloff numbers. I need to whip my mouse for a 180 degree snap-turn and get a clear, crisp picture of my pursuer on that frame, not however many frames it takes for the LCD to catch up to the picture. Any LCD which can actually do that is suitable for gaming, any LCD which cannot do that is not suitable for gaming.