I mean I don't think I see other industries do this, movies and what not, there might be fringe cases but you usually see a lawsuit . doesn't seem like the gaming industry has anything or any reason to not do it

practically 4/5 games have this issue in E3 reveals and all of  the open world ones end up like this.

Video games change in development. That doesn't excuse some of the worse examples, but I don't think that'd hold up in court unless it's advertised as the final build explicitly, then again, I'm not an expert in law so I could easily be wrong.

Plus some movies do have deleted scenes in trailers too, so it isn't quite exclusive to games. Although it isn't nearly as bad as games, that's natural because games change a lot.

am pretty sure they add these scenes in a final cut in movies after theaters. but thats kind of different. you're cutting something not downgrading the entire product here 

I don't really think it's illegal (I'm in the US), but it certainly comes off as shady, which is a good reason not to do it.

There is also the possibility that it's being done unintentionally. Perhaps developers create these games using hardware other than the PS4/Xbone, and sacrifices need to be made in the end.

No, they don't. You are overexaggerating.

Like the other said it is not ilegal because it is work-in-progress. It is bound to change, for better or for worse. Of course you can always imply that it is nasty marketing to show something that most likely not much representative of the final product.

I think they have disclaimers that say that it's not in-game/actual gameplay as a a necessity.

what kind of "work in progress" crew makes art and details that do not make the final version

doesn't it make more sense to start with a prototype then add the necessary details?. we're just making games pretty for the section of the demo. this isn't work in progress crap. it takes work to make the games look this nice and detailed

the developer doesn't get pregnant with a game and somehow start chunking down stuff from it after its born. they put in the work to make it look nice

kind of a nonsensical argument really. movie cut some parts after cinema release because they often don't meet quality standards. and again they add them in blu ray releases if there is nothing wrong with them.

they aren't idiotic. they have development kits to know if the game will run or not on the hardware they have. and often times we get shown a game that is supposedly being run on that hardware.  two things are the only expalantion

1) it costs too much money to make the entire game look that nice and so they just have a vertical slice that they show for the demo that looks that way

2) the system can't run any sort of graphics that looks like that. and its being on on a highly equipped computer and a special build that the consoles and an average gaming pc can't run.

gotta say honestly thats quite an underwhealming and downright pathetic  argument . the computer isn't some godly sentient machine that just makes a game out of thin air and we have a bunch of nerds sitting at desks caring at it to make it low enough for us to run. they make that detail. 

it costs less money to undershoot and then improve. not spend more time and money to overshoot and then carve away at it. 

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.

I honestly think they should label all the footage they show as a "work in progress and not the final product", which in turn tells the audience that what they are showing you isn't the final release version of the game.

That said, I do find myself getting tired of seeing hyped up footage and then the final game not looking close to what was originally shown at e3.