I personally know people that download the games, they later buys, since demos are rare and 9/10 demos show one of the best parts in the game, sometimes the only good part and i find them unreliable, so i tend to go by video reviews or 'lets play' type of videos.
It allows me to see if it is the type of game i will enjoy, it would be cool if it was possible to have an account of the developer's site or something, where it allows you to download a review copy that shows a small portion of the game, that alone would lower piracy to some degree, but there will always be those type of people that are just too cheap and want everything for free.
Its like Teen Wolf for example, the series is awesome, i have series 1%2 on DVD, but the EU people have decided not to pick it up, which means, no tv showing, no DVDs.....for series 3 and 4, i will never get to see, its problems like this that makes piracy so rampant.
I even have netflix, but since i am in the EU, (london) i don't have access to what the US netflix does, all Star Trek Series, Teen Wolf....EVERYTHING, i get some crap shows that got cancelled, another reason why piracy is so bad.
I don't agree with piracy, but i can understand why some do it.