Sometimes getting good grades just means you have a good memory.
Does memory equal creative intelligence? I would say not necessarily.
True to a point. But that's almost beside the point. If you were doing hiring for a tech company, or a bank, or some other concern that needed employees who could work with numbers at a high level, all things being almost equal, would you hire the person with 4.0 in math from MIT or the person with a 2.5 in math from Podunk State College?
You can argue that no two people are exactly the same and it's difficult to compare two separate people in their totality, but I think you'd look more fondly on the person with a 4.0 from MIT.