And given that we now live in an on-line world in which there is practically a cottage industry devoted to spreading spoilers about every high-profile movie in the works ("Top-Secret Toy Designs Reveal Major Plot Twist!"), is it any wonder that the studios have gotten a little more secretive than they used to be? They can't even put out a casting call ("Wanted: female actress to play sexy alien scientist") without setting off a firestorm of speculation and complaints about a movie that might not have even starting shooting yet.
Maybe they don't want the entire internet looking over their shoulders and passing judgement at every step of production? ("This movie is going to suck, big time. They haven't finished filming it yet, but I saw some preliminary costume designs on the internet so I know STAR TREK is dead!")
Lord knows I don't post the outlines for my upcoming novels on-line and let people have at them . . . .