Logically, you are absolutely correct. But if you've seen "80% and more" somewhere, I don't think it's a terribly bad error. There's only one thing it could possibly mean, so it won't cause any problems.
Student or Learner
I would like to know which of the following is correct :
-- you need to score 80 % and more to pass this exam
-- you need to score 80 % or more to pass this exam
To me, it looks like the second one is logically correct. One cannot score both 80 % and above that at the same time. Right ?