If customers are fooled into buying the wrong product, and it would harm the image of the real product, as well as make people more wary of buying the real product for fear of being ripped off.
If someone thinks they're buying the an iPad2 and they actually bought shiity iPad2 knockoff as made by some company you've never heard of in China, they'll probably thing "wow the iPad sucks! I'm never buying another Apple product." This hurts Apple even though they did nothing wrong. By letting them go after people who try to fraud their customers, the customers get protected and Apple's brand gets protected.
Now when they abuse this position to try to monopolize something stupid like rounded corners or page turning animations then obviously its bad for the customer and should be illegal.
Do you really believe that customers who got defrauded are going to actually take the time to sue the fraudsters? Many of them might not even know they were defrauded and the remainder would probably just cut their loses and move on.