Games on Xbox Live can have a maximum of 1750GS attainable, and since the map packs so far have handed out 150G for completion it could hint towards Treyarch planning to make 4 map packs for the game, as 1000 + 150 * 4 = 1600 would fall comfortably under the gamerscore limit set by Microsoft and even allows the last 1 or 2 mappacks to hand out more gamerscore. What I'm slightly concerned about is the quarterly limit of 250G, which could force Treyarch/Activision to publish the fourth mappack very close to the release of MW3, but then again judging by the amount of $$$ they are able to gather into their piggybanks with every mappack I doubt they would not publish a fourth mappack solely because of that. They probably want to squeeze everything they can out of Black Ops before MW3 comes out.
From the Xbox Live article in Wikipedia:
Hopefully I didn't misinterpret that!