Both games require new Recognizers, their own HandEvaluators, and new procedures for dealing and playing. But common aspects are inherited from superclasses, so the OOM programmer only needs to worry about the differences between each game. No complexity wall is encountered. The traditional application is initially easier to create, but starts to fall apart when adding features and reusing code in new contexts. The object-oriented solution takes longer to get off the ground, but sails smoothly past the complexity wall.
Encapsulation enforces modularity and reduces problematic dependencies between objects.
Polymorphism and inheritance enforce reusability.