I always thought that content-centric was the easiest for people to deal with, i.e. "I want to change this document", and not "Let's run this app so I can then change that document".
It seems that the popularity of iOS (as opposed to say Windows or MacOS) proves otherwise, everything is an app. Windows 8 is also becoming app-centric, and MacOS is also moving in that direction (LaunchPad shows apps, not your documents.) Perhaps using tools is in our genes?