Currently, the options are limited to subwoofers and the rear speakers. Even in these instances, although the audio signal information is transmitted to the sub wirelessly, the subwoofer still requires power from an AC outlet. The wireless surround speakers need to be powered as well. Most likely in this case, a separate, smaller amplifier, plugged into an AC outlet is connected to the rear speakers with speaker wire. This enables surround sound without the need for wires running across the room from front to back.
wireless vs. wired
The small amplifier can be hidden in the back of the room near the speakers, or under the home theater seating if you place the speakers directly behind the listener.
Depending on your home theater design, wireless surround sound may be the right way to go.
For those situations, where wires across the room present the biggest challenge when installing surround sound, this "wireless" option should be helpful.
