Most TFT's are sold conforming to ISO 13406-2, which basically states that its accepable to have 2 dead pixels per million pixels, or 5 sub-pixels per million.
Full details here
http://www.autdirect.co.uk/acatalog/ISO_13406_2.jpg
Even dead pixel g'tees only ensure there are no dead pixels *at the time the display was sold*. Any that appear afterwards aren't covered.