Mac OS X is going in the same direction as the iPad. Mac OS X Lion is another step in the road to a new—or better said, renewed—computer interface paradigm: Modal computing. And along the way, they are taking some of the most successful parts of iOS, like the App Store—with automatic installation of applications—and the springboard—rechristened launchpad in Lion. They are also introducing new user interface elements, like Mission Control.
All apps would be able to have Full Screen mode integrated. That doesn't mean windows are disappearing (yet), but this is clearly enabling the way to full modal computing—which is clearly indicated by the user interface in iLife'11.