Yeah that satement was too generic and was likely more of a 50% improvement over the previous generation as a whole from what reviews show (as it seems to beat GX2 soundly in games that don't scale with SLI, and not so well versus some that do so ~50% average over GX2 is pretty good).
Looks like the GTX280 provides a small improvmenet at < 1920x1200 resolutions but really begins to shine at higher settings