To a certain extent, yes. Can you get into a top-bracket college with a 2.0 GPA? Possibly, but it would be a lot easier with a 4.0 or higher. Can you land a great job without a degree from a top-bracket college? Very much so, but it would definitely help to have that degree from the top-bracket college.
It's a ripple effect, and so the easiest way to stay near the top is to keep up good grades (and striving for good grades is a good way to learn new skills, and especially a way to exercise your short-term memory skills and comprehension, which are invaluable in the workplace).