Unfortunately many televisions and A/V receivers turn off their network ports when the device is powered off (in standby). Because of this, they are not listening for commands over the network.
Some devices may have options in their menus for standby power state such as power saver, fast start-up, etc. While there is no guarantee, changing these power settings may allow the device to power on from standby by keeping the network port active in standby.
Another option to consider: Many newer TVs have an option to allow external devices to control TV power through the HDMI ports. This is via a standard called CEC (Consumer Electronics Control). Consult your owner's manual to see if your TV might support this feature and how to enable it. Different brands refer to this ability by different names. From Wikipedia:
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), INlink (Insignia), 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).
As an example, on my Panasonic Viera TV, powering off the DirecTV receiver does not affect the TV's power, but I am able to power off the TV using network control anyway. My particular TV will not power ON using network control but turning on the DirecTV receiver does in fact turn the TV on for me automatically with VIERA Link enabled on the TV!Tags: Power ON