Uhm, the rules say:
If this would be applied to games, discussion of games would then ofcourse be impossible.In sum, a spoiler is:
Any form of information that has not yet been mentioned in the anime, regardless of source.
Any such form from an anime episode that has not yet been subbed (in english)
Also spoiler tags are usefull for collapsing the occasional wall of text some users produce or for collapsing pictures that would normally be too big for the layout.