HDMI has a feature called CEC which can control inputs, volume, channels, basically everything a normal remote can, but over the existing cable and connection. https://en.wikipedia.org/wiki/HDMI#CEC
http://manuals.playstation.net/document/en/ps3/current/setti...
AFAIK, the PS3 is the only current generation console to implement CEC.
From the Wikipedia page linked by the parent:
Trade names for CEC are Anynet+ (Samsung), Aquos Link (Sharp), BRAVIA Link and BRAVIA Sync (Sony), HDMI-CEC (Hitachi), E-link (AOC), Kuro Link (Pioneer), CE-Link and Regza Link (Toshiba), RIHD (Remote Interactive over HDMI) (Onkyo), RuncoLink (Runco International), SimpLink (LG), T-Link (ITT), HDAVI Control, EZ-Sync, VIERA Link (Panasonic), EasyLink (Philips), and NetCommand for HDMI (Mitsubishi).