GT5 will make it because of online play. When your not a huge racing fan but 3 of your friends have the game and are telling you to get it so you could race with them online it could very easily push many people over the edge who normally would not have bought the game on their own. That on top of the already huge fan base (even if it is diminished some from where it once stood)would make it a 10m seller I'd think.
As for MW2, going by my basic 1/3 rule for sequels (1/3 of lifetime sales happen week 1, 2/3 by week 10) MW2 will fall just short of 10m but since it's just an estimation I'd say it'd have the legs to surpass 10m since the publisher/retailers would still be selling the games long after most games would be done because of it's popularity.
