Anyone who had to deal with a 5.1 setup knows what kind of hassle cables can be. Polk Audio is trying to make things better with the PSWi225 Sub. It uses a 2.4Ghz wireless transmission to avoid using a wire to the 5.1 box. Now, that doesn't spare you from having to plug the power to an outlet and some cables that go from the wireless receiver box to the Sub itself. You're basically saving the connection of two thin cables.
Unlike rear speakers, Subs are usually next to the 5.1 box, so I'm not sure how much this actually helps, but who knows. What we really need is wireless power AND wireless audio. (via widescreenreview, specs in PDF)