I don't think classes are being thrown out all together.. why 3.0 jobs don't have classes, imo, is based out of necessity

1. level increase to 60
2. 3 new Jobs being introduced simultaneously

In the PAX interview YoshiP mentioned how difficult doing 3 new jobs at once was for the battle team. I think they have gone this 'no class' route for these 3.0 jobs specifically to ease the balancing issues that arise from creating new classes.

If these 3 had base classes, then the battle team would have had to QA Test all 3 classes as well as the 3 jobs. This task becomes exponentially more difficult when you consider that classes have access to ALL cross-class abilities.. I think they did it this way just to make their job easier, and to get the new jobs balanced and ready for 3.0 launch on time.