ACT or SAT = 4 hour snapshot
GPA shows the consistent actions that lead to success in class. A kid who is present, prepared, participating, and performing will earn a good grade. It's the Four P's, and they determine success at the high school level, the college level, the professional level, and so on. Grades earned will always be a higher consideration in the college admission process than standardized test results.
In the case of atlcougar's son, having an unweighted GPA that is a tenth of a point below the average is going to be the biggest red flag in any Admission Committee. It is NOT to say that this isn't an OUTSTANDING young man. It is only to say that the biggest academic consideration was not in his favor.