LED TV may just be a temporary move until OLED TV comes along.
Looking at the soon to pass regulation in California banning large power consuming TV, LED TV has lower power consumption. But to increase contrast, some of the LEDs for backlighting have to be dimmed or use fewer LED by locating them only at the edge which also makes the TV thinner.
LED TV does not have mercury as in LCD TV, however they compete for scarce natural resources like galliium and arsenic which are also used in some type of solar panels.
OLED will be a true LED TV, not a backlighted one, but I do not know where they are with improving life on the blue OLED. Anyway, that is just a function of R&D investments and time.