I think we're all conflating "worst case" with "common case" of Save As and Duplicate.
In the worst case, the traditional filesystem behavior could lose your data if you accidentally hit "Save" instead of "Save As". In the common case, it let you save off new versions without affecting your existing version.
The (Mountain) Lion paradigm removes the worst case; you can always revert and recover. But the behavior of the common case gives the appearance of lost data, and violates both Principle Of Least Surprise and Do What I Mean.
In the worst case, the traditional filesystem behavior could lose your data if you accidentally hit "Save" instead of "Save As". In the common case, it let you save off new versions without affecting your existing version.
The (Mountain) Lion paradigm removes the worst case; you can always revert and recover. But the behavior of the common case gives the appearance of lost data, and violates both Principle Of Least Surprise and Do What I Mean.