RF, once touted as the ultimate home-networking standard, has been wiped out by Wi-Fi, but newer technologies such as ZigBee and ultrawideband are now in the running too.
The primary difference between the HD and XD models still appears to be the latter's ability to push out 1080p video, while the XS adds a USB port and gets a spiffy new RF remote, which we're hoping takes a cue from the Boxee clicker.