I figure that it's polite to avoid public spoilers (twitter, facebook, talking to people without checking if they've seen it yet) for a reasonable amount of time. For a TV show - about 36 hours to cover different time zones. For a newly released movie - a few weeks. For a newly released book - about a month.
That way if someone really wants a pristine reading/watching experience they've had the opportunity to do so.
The flip side, of course, is that if someone wants a pristine, unspoiled experience with a newly released piece of media, they need to make an effort to see it quickly, and in the case of TV shows should probably avoid twitter and facebook while the show is actually being shown. Recording Game of Thrones on Sunday, with plans to watch it the following Friday, and expecting everyone to keep the events secret is not a good strategy if unspoiled viewing is very important too you.
(GoT is an interesting case, in that it's possible to spoil it before it airs, based on the source material. I knew that the Red Wedding was coming, and which episode it would show up in. I know at least two major shocking plot events that will probably occur next season (heh, heh, heh)).
The example given in the OP was *not* a spoiler - that was pretty generic information about the style of the game. Anything shown in the trailer or 'next week on' doesn't count as secret material. It's not a spoiler if you're discussing historical events (the ship in Titanic sinks!)
And if you get upset because someone just spoiled The Sixth Sense or The Crying Game for you, you're going way over the top. There's definitely a statute of limitations on shocking twist based movies or books.
FWIW, I live in Asia, and I get some stuff at the same time it's released in the US or Europe, but for other stuff it can be months to years before I get (legal) access to it. I just accept that as part of life here.