We just recently purchased a 50" Panasonic HDTV. The sales associate sold us a $75 HDMI cable. Is this necessary? We're not really sure what this is for, as we don't have a clue about this kind of stuff. If the HDMI cable is necessary, is one that costs this much necessary? We haven't opened the package yet so we can return it and look elswhere for something cheaper if it is needed. Thanks!!