For one thing, might that be part of why among freeware Tetris clones, clones released as free software (such as M-x tetris) have historically been least likely to draw nastygrams from The Tetris Company? For another, iOS itself has the same ethical problem as any other platform without the ability to install self-signed software, and cloning an iOS-exclusive game frees its mechanics from being tied to that platform.
A valid point, but you contradict yourself. If there already exist two implementations of (roughly) the same game which both run on different platforms (presumably one of which is a Zynga target platform), Zynga aren't "freeing" anything.
As an aside, I was interested in the Tetris IP arrangements so I searched around and found this Quora question. Can you guess who wrote the first (and current top rated) answer?
Seth Sivak, PM / Designer @ Zynga Boston
Oh the irony. But I digress.
But how is that practical? After some point, all the possible mechanics within a genre have been tried. Everything is just a different combination of the same elements, and one might end up combining them the same way someone else did. The last genre launch I know of was a decade and a half ago with Parappa the Rapper.
To claim that Zynga were just "throwing shit at the wall" and managed to create a 1:1 copy of Tiny Tower strains credulity. I know getting past the "threshold of originality" is practical because so many game developers manage to do it year after year. As hardware and user interfaces evolve (think touchscreens and accelerometers), there are more and more opportunities for companies to put forward unique and original experiences tailored for new devices. I highly doubt that the pool of available original game ideas is even finite, let alone close to exhausted.
To compare operating systems with games based on the criteria of originality completely misses a key difference between games and operating systems. When it comes to OSes, most users absolutely *detest* change. They can, and *will* simply ignore your product in order to stick with what they feel comfortable with. Take a couple of Microsoft examples: Vista and the ribbon UI. Both of these were widely panned by users, to the point that many people threatened to do away with using Windows altogether. But they stuck with it. Why? Microsoft certainly didn't keep their customers because of a lack of worthy commercial and non-commercial competitors, and they didn't keep their customers by immediately caving in to user demands (even if they wanted to do so, their distribution mechanisms and release cycles were far too rigid to undo their UI changes at the click of a button). Microsoft kept their customers because they had a platform, and on that platform they and others had built applications which Windows users had become attached to. Sure, everyone could have switched to something other than Windows, but that would have taken time and had a steep learning curve. The real winner there was Windows 7, because it had the shallowest learning curve available and virtually zero cost of migration for most business-critical Windows apps (which are usually more expensive than the OS itself). The lesson is that if you want people to jump ship to your OS, you need to make it as easy as possible for them. This is why (IMO) GNU would have failed if it modelled itself on anything other than the dominant (or near-dominant) OS at the time.
Games are different; your average gamer doesn't care whether or not they'll have to upgrade to QuickBooks 2012 if they buy a copy of your new game. They just want something interesting that they haven't played to death yet. In addition, moderately steep learning curves for games are often valued (think StarCraft 2) as they reward players who put effort into learning the ropes. Zynga aren't going to sell their new game to any of those Tiny Tower fanatics who change their iPhone's clock forward a few hours between restocking to make sure their skyscraper empire is progressing as fast as possibe (you all know who you are). Zynga are targeting people who have no idea what Tiny Tower is. They're using their well known name and massive resources to try and get on that sweet sweet Tiny Tower gravy train. Nothing of any real value is produced, and Nimblebit gets completely shafted by a company who could be doing more productive (and less ethically questionable) things.