The dilemma of copycat games has long been purely an ethical one and rarely a legal one, but perhaps we’re speeding towards a court-ordered stance after all these years of gentlemen’s agreements and surly acceptance. Patents, trademarks, code and artwork have been protected, but ideas haven’t. Should they be?
As Colin noted, the games industry needs to be able take ideas and build on them, twist them around, and make something the creator considers to be one better. That’s exactly why you can only protect the implementation of an idea and not the idea itself, and it’s largely what “creativity” generally means. Games aren’t unique in relying on “weak” intellectual property laws in this regard: fashion, food, music, magic tricks, and in fact, design in general all work in this way. Without this setup, as a simple example, Gimme Friction Baby would not have spawned Orbital. It’s how genres such as “autorunner” come to be.
Where we run into real problems is in the situation of “The Blocks Cometh and, er, The Blocks Cometh”, where someone is selling an iPhone version of a Flash game without authorisation, using all the original graphics and design elements. That’s counterfeiting, a “fraudulent imitation of something else”, to quote the OED. And this is where the “strong” intellectual property laws of copyright, trademarks and patents come into play. If you own copyrights and registered trademarks, you can prevent counterfeit games trading off your success.
I’m not a lawyer, so this is most definitely not legal advice, but, as an IP owner the onus is very much on you to enforce the protection provided to you by law (it’s certainly not up to Apple, as GI.biz imply). If you choose not to enforce that protection, you’re giving tacit permission for the counterfeiter to carry on. Worst case scenario is if you ignore some cases and try to enforce others, you may well forfeit your right to legal protection altogether.
In short, if you have something you think is worth protecting, you’d better figure out how you’re going to protect it.