Light can, and has been, made to go slower and faster than c, as is explained in the articles you linked to. As to why light acts in the "reverse direction" as explained, you can't get much better than "because it does". You can create analogies to explain what's happening, but there's no explination as to why. These experiments to me say that light is in fact a physical substance, though I could be wrong I'm a casual physist at best.