They're for everybody, but one of the most important things to note is that if a person who is single has an income above $15,000 a year, the person is no longer entitled to receive the GIS. Then there are different categories, and the thresholds differ with respect to whether a GIS recipient is married to a non-pensioner, or if the GIS pensioner is married to another GIS pensioner. The income thresholds will vary in those cases.
On February 20th, 2007. See this statement in context.