No it doesn't "need" to rely on trailers. If anything at all great trailers get the player pumped up for the game. You're assuming that there lies an expectation b/w trailer and gameplay. However our minds can easily grasp the intention of the trailer and take it at face value while only attributing our excitation for the game and not some illusory expectation due to a misinterpreted perception of the game. This has always been the case but I do understand what you're trying to get at in this article, it's just that it's not true. Perhaps think about the opposite effect and ask how much trailers provide and link an emotional attachment to the overall feel of the game. Gears of War 1's mad world trailer gave me a much stronger connection to the feel of the game than other trailers that had no emotionally artistic music or not much artistic nature in general.