This is false. Grades correlate reasonably well with ability. Plenty of people get good grades without corresponding ability, but 99% is a laughable exaggeration.
What would be evidence for that statement, in view of the parent comment to yours that disagrees with that conclusion? Where would one look for research on this issue?
One old book that I read back in high school days
http://www.amazon.com/Wad-Ja-Get-Grading-Game-American-Educa...
suggested that grades correlate less well with ability (or any other meaningful characteristic of students) than supposed by the teachers who give grades to students. I'd love to hear about current research on this issue.
... as measured by grades.
Now, I'll agree that grades don't correlate _perfectly_ with ability for _everyone_ - we all know the bright slacker who doesn't turn in his homework, and maybe skips a test or two. But, in general, a student who score 95% in physics knows their material very well. A student who scores 15% in physics is probably clueless.
Physics classes don't prove a blanket statement regarding grade quality over all subjects, any more than Yao Ming proves that Chinese people tend to be seven feet tall, or the King of Sweden proves that Swedes tend to be kings.
This is especially true of people who make a living from ostensibly being clever. Some of us, clearly including myself, are insecure.
And, since no one ever gets screwed, we can therefore conclude that your original argument is correct!
(See also: http://en.wikipedia.org/wiki/Appeal_to_consequences)
Demonstrating anything beyond that would require proof, hence the burden of proof is squarely yours. :)