Think about it: what does a grading scale really mean? What does a grade really mean? Thise things vary from school to school and from class to class - something the Office of Admissions is aware. Whether your school gives an A for 93+ or 90+ is irrelevant. Did you know some countries have 20-point grading scales? Did you know that I've had classes at UVa with average and median grades in the 60 range. What do you think of that?
I don't know why so many highly intelligent kids on this site get so wrapped up with silly things. Perhaps it's because they lack the right kind of perspective. Why on earth does it matter if FCPS doesn't allow for the 4.5+ weighted GPAs? Why do people post their weighted GPAs when asking for chances? Admissions doesn't really care. That weighted GPA is only a tool used by your school to rank you among your peers, or in some cases, to standardize your performance in some other way.
Read this article on grades:
Grade (education) - Wikipedia, the free encyclopedia
Crazy, huh? Do you suppose that students from some of the systems described disadvantaged versus each other? No, they're not. Grades are meaningless outside of context and have no intrinsic, absolute value.