People would need a lot to start using facebook like Twitter. They'd need to be able to get all of the statuses via SMS, Firefox Extensions, etc, etc.

People overall don't use Facebook statuses like they do Twitter, and that inertia will take a lot more than allowing people to make apps that would show people their friends' statuses.

Inertia is a powerful force, and that larger userbase would somewhat be a disadvantage in that regard. It's more people they have to get to switch over to using statuses like they would Twitter. Getting that process started would be almost impossible.