I always go into LP's with as little bias as possible, usually because the game in question is one that I know little of, and if they're people I watch often it's for their commentary more than anything. However, there are many, many LP's that have persuaded me to buy a game, such as Bioshock Infinite, Dragon's Dogma, and most recently, Legend of Mana (or games that I still want to buy: looking at you MGR:R, Okami, and NieR!) I feel that LP's are one of the most effective advertising tools in the industry--more so than 30 second commercials, at least--as they can make a person think, "Huh, so that's how this game plays. Y'know, if there's a demo, maybe I'll try that." Or if there is no demo, then they might watch the LP a little more and decide they want to buy the game and experience it themselves. And if they don't like the game? No sweat. Their money was never going to the game anyway, so it's no big deal. If they were going to buy the game, but the LP turned them off, once again, no sweat. It's one person. And if the game's bad, who's to say that weeding out bad games is a bad thing?
So I cannot fathom why Nintendo would do something so stupid. As a previous poster said, Nintendo tends to offer at the very least well-made games, and so it's as if they're saying, "We don't want you to show our games to prospective buyers, and we don't want other companies to pay you money to show off our games so that we don't spend a dime. We'd rather take your money or force you to stop advertising our products for free." It's insipid, completely and utterly insipid.