Different sources vary a bit about the time the spoilers occurred but the Sub Emissary cutscenes were leaked to the Internet, either before the game was released or very shortly after, through platforms such as Youtube, which was not taken well.
“Unfortunately, the movie scenes we worked hard to create were uploaded onto the internet. You can only truly wow a player the first time he sees [a cutscene]. I felt if players saw the cutscenes outside of the game, they would no longer serve as rewards for playing the game, so I’ve decided against having them [for the upcoming Smash bros.].”
It is easy to find video game footage on the Internet, either it be cutscenes or direct playing sessions. I do not believe Sakurai is reacting simply because some people may find them at some point. I think it was more a matter of how fast it would happen. Super Smash Bros Brawl was really hyped and I am sure many players completed the Subspace Emissary a few days after purchasing and uploaded those beautifully crafted scenes to the world wide web. Unfortunately that gave them prematurely world wide exposure and people learned about their existence while having access to the entire story before the majority of players had the chance to finish the games for themselves.
Still, while I can sympathise that the surprise factor only happens once, I think players react differently and seeing them on Youtube even by accident could fuel their desire to continue because there is still a pride on having them in your living room Television because of your progress that makes them feel like ‘the real thing’ and as a gamer appreciate more than watching the video. I feel that in the end, it is the choice of the player whether he/she rather or not to be spoiled and it saddens to know that this decision went as far as probably taking off the Story Mode as a whole.
There is no doubt that the team really spent a lot of time and effort putting together the story, levels and cutscene animations, and that Brawl’s one player mode has been the most complex we have seen to this date of the series. Perhaps it is a step in the right direction to keep some of the simplicity of its humble beginnings when it comes to the lone player modes.
It is not all doom with the cutscenes though. Sakurai knows we reacted positively and acknowledges their power to go viral, so he plans to use the cutscenes for other things which their team will actually be happy to see being spread, such as the latest ones we have seen introducing new characters.
While the Story Mode and cutscenes that we know of from Brawl will be cut off for the newest installment of the game, we can be relief as Sakura has expressed that there will be a new feature that will be included which will be separated from the standard versus play mode.