Point taken, and in fact Burnout Paradise could very well be the guinea pig for the new business model, so-to-speak. It's easier to justify the charges for the additional content in that game, however, as the additions are very evident: new cars, new gameplay modes, new worlds, etc. Similarly, when I buy new content for Rock Band, the content is very evident, as there's new songs to play.
I'm not sure such a system would go over well in a sports game when we already expect working and well-tuned franchise modes, frequent internet roster updates, and innovations over last year's game out of the box, and all for no more than the initial $60 charge.
I would consider paying a monthly charge for something superbly ambitious in a sports game, such as a persistent massively multiplayer EASFL where I control one character with many other players, a la the EASHL, but also where there would be owner players do not play per se but who manage team rosters, buy / sell / trade players, draft new players, etc.