That is to say that light propagates at the same speed as a gravitational wave. However the gravitaional wave gives location of it's source at an almost instantaneous fashion, while a photon gives it's location when it slaps you cross the face with the source. In an example with the sun and Earth. The sun will be seen by us as to it's location eight minutes ago. The light waves become independent upon leaving the sun, and thusly it's location is pretty much set in stone. In the case of a gravitational wave - The source of the wave remains on the sun or Earth. When a gravitational wave passes you on Earth from the sun. It in effect is the extention of the source, and that extention moves with the source while the extention has a speed limit of C. In other words a gravitational wave that effects you from the sun is eight minutes old, but since it is an extention of the source ....The source location is known instantaneous, because the extention moves with the source. This illustration is of two gravitational waves. One from the sun and one from the Earth. Each wave is drawn as a spiral pattern. I.E. The source is connected to any point on the spiral. http://home.att.net/~jrabno9/g.jpg When the source moves it's location is known instantly. but not it's distance. Such that should a source move in a lateral direction to another source - The extention of that source moves with it without exceeding the speed limit of C.