It's a perturbation in time. C++ uses the virtual keyword and final as default.
Java follows C++ and attempts to take the best and improve on its shortcomings. The dangers of overuse of inheritance haven't come to light, so Java chooses to use the final keyword and virtual as default.
C# follows Java and has the benefit of hindsight. Anders chooses to go back to the C++ convention after observing Java's experience.
