Agnostic has a post up where he ridicules the taboo against spoilers as a sign of deterioration in entertainment, an increasing vapidity among those who take it in, or both. It strikes me as a sensible response to a changing media landscape, as I tried to flesh out in the comments, which are reprinted here:
I don't think the insinuation that wanting to have a conclusion withheld is fairly described as hysterical, nor is it a sign that the narrative is trash and/or that the viewer is trash.
I regularly record NFL games and watch them later in the day, not because football's sole appeal is what it reveals about the standings or because I'm incapable of appreciating anything other than who gets the win, but because it takes away from the overall experience. I'll still watch Briggs and Urlacher in Miami whether the Bears stay on top of the north or not. I'd prefer not know until the end of the game, though.
That you wouldn't structure your argument around a sports contest hints at a significant reason for the rise in spoiler-phobia over the last 15 years. Sports have always been spoiled immediately. The assumption is that you take it in in real-time, or you don't take it in at all and instead settle for highlights on SportsCenter. Episodes of TV series used to exist in the same way. Now, though, viewers of TV shows are not beholden to see something at the time it is slated to air--they are easily able to access it at their own convenience, by buying entire seasons on DVD, viewing them on youtube, etc (to a lesser extent this applies to sports as well).
In the past, after the show or event aired, if you missed it, it could be fairly assumed you would never see it (at least not anytime in the near future), so revealing the narrative wasn't nearly as big of a deal. It was as though if you didn't read the book within a specific time frame, all you had access to were the Cliff's Notes--no harm in reading them in such a situation. But if you are able to pick up the book at your own leisure, your aversion to the Cliff's Notes prior to reading the book yourself is understandable.
While the term "spoiler" may have been born in 1995, the disdain for it obviously predates that time. In the Simpsons episode "I Married Marge", aired in '91, a teenage Homer enrages a line of moviegoers when he expresses his surprise at the ending of The Empire Strikes Back to Marge. The difference then was that unless you went seeking a movie's conclusion, you wouldn't find it (absent some loud-mouthed jerk blabbing about it without solicitation). Fast-forward to the age of Google, blogs, and social networks and the chance of having something spoiled is everywhere and unpredictable. It can be difficult to escape from. Spoiler warnings have become a necessity because of technological change. That seems a sufficient explanation to me.
Regarding video games, I think you have it exactly backwards. The aversion to spoilers is a sign of how much more stimulating narratives have become and how video gaming has evolved to the point of realizing the same character depth, philosophical speculation, cultural and historical referencing, and moral instruction that movies do.
The revelation that Samus is a girl is the ideal illustration of a vapid 'shocker'. It has no bearing on anything else to the gameplayer. The tragic role reversals of Tidus and Yuna (Final Fantasy 10), in contrast, is richly teased out over 40 hours (another reason video games, and rpgs specifically, are so spoiler-adverse--when it comes to time and depth invested in a narrative, other forms of entertainment pale by comparison), building steadily but so subtly that at the story's conclusion it still leaves the gameplayer reeling. Tidus is initially an ego maniacal, vain sports star; Yuna a prophet-like, almost messianic young woman guided by the Fayth (angels) toward the ultimate (and presumably preordained) sacrifice as a means of joining Sin and removing it from the world.
As it turns out, it is Tidus who inevitably must be sacrificed. Tidus, of course, struggles mightily with this, but so does Yuna, not just because someone else must suffer what was thought to be her fate, but because she must come to terms with the realization that what she believed to be the culmination of her existence was an illusion, and that her new reality was entirely at odds with everything she'd lived for up to that point. There are enormous statements made about religion and its interaction with both society and the individual made in the game. That is just one of many remarkable elements of the narrative. Knowing as much in advance negatively alters the experience of the game far more than knowing Samus' sex does (although neither spoiler makes the games unplayable by any stretch--they survive on far more than their narratives).