Firstly, even if USC was the unanimous number one consensus choice among all media outlets in the universe, it wouldn't mean all too much until the games themselves actually started. That being said, these sorts of things serve as a gauge for what the wider audience as a whole feels in terms of the pulse of the current state of college football.
It also, more importantly, gives the current perceived outlook of the Trojans. This is something that can affect recruiting and the reputation of the program.
Cleveland.com was the organizing entity that polled writers from across all teams in the Big Ten.