Intention of College Football Ratings

Tries to get best fit to current season's data Tries to produce ratings useful for predicting future games
Determines which teams had the most impressive season Determines which teams are strongest
Does not publish predictions Might publish predications
Does not use data from previous season Uses data from previous season early in year to avoid bad predictions from insufficient data
Early season ratings don't mean much because of lack of data (some systems don't publish early in the season for this reason) Early season ratings are meaningful
Has no preseason ratings because there's no data Might have preseason ratings
Might be based on win/loss record only Systems serious about predictions usually use the margin of victory and maybe home field advantage
Judged by how well past results are fit. For example, what % of games were upsets based on the current ratings. Judged by how well the predictions work. For example, what % of games were upsets based on the ratings from the day before the game.

Predictions are for entertainment purposes only.

Thanks to David Wilson for his explanation.