It doesn't even have to be the valedictorians. I got B's and C's basically without studying until college. I had to learn how to study in college. We even had an introductory "how to study" class in college because it was such a problem. I was always told that "HS is hard, you can't just breeze through it", which was completely untrue, and I absolutely breezed through it. So I thought the same thing would apply to college, which it turns out, actually is hard.
This is exactly my story as well. Even in HS, if I studied for an exam it would be a couple of hours the night before. Not so many A's maybe but plenty of B's and C's got me through just fine. Then it was quite a shock when I got to college/uni and learned the hard way that in many cases it took weeks of studying for an exam. Now in retrospect I'm quite proud of myself that I didn't give up. There were certainly times when I felt like doing just that.
I agree. In undergrad Computer Science, I had my first "Oh sh*t" shocks. (My undergrad was a large state school, so I could coast outside of CS) I got a few more in grad school in other subjects.