Surprised no one saw this yet ...
Firstly, the developers have been busy testing various plots and have even considered having the entire world unlocked for the player at the start of the game. GTA veterans will know that one of the staples of previous GTA games has been locked areas that can only be accessed by progressing past certain missions or pivotal story elements.
Some fans enjoyed this system, as it gave them incentive to move through the story and continue playing the game, while other fans found the system somewhat limiting and unecessary.
Secondly, and more importantly, Rockstar is aiming for a multiplayer component to compliment the singleplayer, with up to 16 players fighting it out in various multiplayer modes.
Threads of Interest:
The Movie Thread: http://www.vgchartz.com/forum/thread.php?id=6880
The Crow Eating Thread: http://www.vgchartz.com/forum/thread.php?start=0&id=3886
The Betting Thread: http://www.vgchartz.com/forum/thread.php?start=0&id=7104
Custom GIFs Thread: http://www.vgchartz.com/forum/thread.php?id=18963
The Greatest Game Ever Conceived On Any Platform
Tag: "I have tasted Obi-Wan's bitter tears"