> protection against things that could be reasonably
  > mistaken for them

That sounds more like trademark law.

That said, Apple has to incur a bit of penalty here for being first-to-market. Since the iPad was the first-to-market and the most widely recognized brand, it would not be uncommon for someone to see any tablet (regardless of design similarities) and say, "Is that an iPad?"

It's like Henry Ford claiming that no one else can make cars at the genesis of the Model-T because cars in general are associated with the Ford Motor Company. It would be ridiculous to say that anything with 4 wheels and a combustion engine might be mistaken for a Ford, therefore Ford is the only one that can make cars.