In order to display a HD Ready sticker the screens HDMI/DVI inputs have to have HDCP (amongst other things). If you are sold a TV with a HD Ready sticker that cannot handle HDCP signals then you have a case to get your money back.
Theres a quick summary of the requirements before a set can display a HD Ready sticker.
http://www.dvdlibrary.co.uk/hd_ready.htm
Your screen only has to be able to display 720 lines, it does not even have to be able to show all 1280 pixels making up each line!