Shadowstalker16: That is because the medium they sell is visual and or auditory in nature. Games are interactive and with open ended levels. In a pirated copy of a TV show or music track, you can get the experience you get with the original. But games on youtube aren't like that. You can't get the experience you would've got from the game if you watch a playthrough of it on youtube.
Elmofongo: I call that into question. Because you imply every game yields a different playthrough. Well let me tell you. I have played many kinds of games in my lifetime and I came to the conclusion that no most games still yield the same playthrough. I have played games like Resident Evil 4 for so long that everytime I play it its the exact same playthrough. A Call of Duty campaign the same playthrough. A point and click adventure, depending on the kind it can result in the same playthrough.
I also call into question that people says Let's plays are free advertisments that makes people want to purchase the game if they like it enough. You imply that no one watches a let's play so that they don't need to buy a game? Thats to good to be true I am certian people these days only just watch let's plays and not bother buying games at all.
Elmofongo: Whatt I said.
You can "call it into question" all you like, but ask any big Youtuber like Totalbiscuit, Angryjoe, or Markiplier just how many people have sent them messages in the past saying that they've bought a game because of their videos. Developers have even gone on record to personally thank Pewdiepie for a huge influx of sales on their games after he's done a video involving them. The evidence is all out there. If you watched the podcast that I linked to earlier in this thread, then even the small-time Youtubers with few subscribers that just barely make a living are flooded with messages from viewers asking "What game is this? I want to play it." So, in order for your argument to work, then they'd all have to be liars.
Personally, I don't need the play-through of a game to be different than what someone else has played, because I don't care about story in a game at all; gameplay is king, and I'll suffer through horrible story and voice-acting if the game is fun. The only games where you get the entire experience by watching them in video are point-and-click adventure games and games with very little interactivity, like The Stanley Parable. How many point-and-click adventure games has Nintendo made? Also, here's a spoiler for you: In the next main Mario game, Princess Peach is Kidnapped by Bowser, and Mario has to rescue her (probably.) Have you gotten the whole experience of the game now that you know the story? If not, then that means there must be something more to games than just the story, unlike a book or a movie where if someone spoiled what happens, then that's all there is to it; because with other mediums you are nothing but an observer, but with video games there is a level of interactivity unseen in other mediums; an element of doing, rather than just seeing. Rather, you see something
because you do it, and that's what separates the two. To finalize the perspective, I personally don't enjoy movies or books anywhere near as much as games, because it's that level of interactivity that separates the mediums that makes gaming appealing to me, so of course I need to buy the game in order to get the interactive experience that I desire, even if I do watch a video of it.
I bought more than half of my collection of games only after getting to see a video on Youtube of how it plays. I never buy a single game anymore without watching video footage of it on Youtube first, because I've gotten burned by advertising and I only trust my own first impressions from watching the game with all of the bugs, glitches, and un-fun parts intact, now.
I can think of quite a few games that I would never have touched had I not seen someone else playing them and realized how much fun they looked. Watch
http://youtu.be/ToUt1X3JbmQ?t=1m10s from the point that I started it at to the end of the player's turn. I bought that game after initially writing it off because I watched those guys play all of the different games and modes, and it looked like a blast with friends. Can you honestly say that your experience would be no different with friends? Can you say that you couldn't enjoy the game anymore if you purchased it after watching that? Even if you don't like that particular game from the video, then the same thing is still applicable to many other games out there.
You might want to actually ask people who watch gameplay videos and let's plays about their purchasing habits and their experiences before claiming that you're "certain" of whether or not they buy the games that they watch.