I think this is an issue with a lot gray areas as far as the law is concerned. On the one hand, you're showing a product that is still in development. On the other hand, if the final product is worse than what the consumer was initially promised, then that could be grounds for a lawsuit. I think what is important is to determine wether the publisher and developer had known that their final product would be watered down and downgraded.
With a game like Aliens: Colonial Marines, it was a clear cut case of the developers deliberately lying to the consumer about the final product, even leading up to the game's launch. Other situations are not so clear, like with Watch Dogs, where the game that Ubisoft showed at E3 was real. The problem they were showing a PC build of the game. The PS4 and Xbox One could not replicate that same performance. However, those versions would sell more than the PC version, so the PC version was watered down so it wouldn't make the console versions look bad. In that case, Ubisoft did not lie when they were at E3. Apparently, at the time, they thought the PS4 and Xbox One would be able to do better. At the same time, they did not deliver what was promised, though apparently the PC version can be hacked to unlock the advanced graphics that were initially promised.
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