While I agree that what you say is correct and that percentage does not determine your intelligence courtesy to our education system, but this does show a person's dedication and speak for a person.
This is a criteria to determine the dedication and hard work an employee can put because of the consistency he has shown in his past. and again this is not a Hard Fact.
The reason why companies look for that while campus is because they want to know how serious you are about your career to make an effort to study.
As in the film 3 Idiots, people do not study to learn, they study to earn!!!