The panel is still a basic TN one with a CCFL or LED backlit option.you forgot led
plasmas (perhaps) require more R&D, and tend to last longer than LEDs/LED-LCDs. manufacturers in these times are not surely looking forward to sell something that would last long to a customer. as sarath said, other TVs can be produced with lesser input to gain high output.
Plasmas have a lower life than LCDs do. This was marketed heavily but the problem is no one calculated the real life scenario.
For example, a crude one, take a LCD which lasts 5 times as long as a Plasma. Now let the Plasma have a life of 5 years. Which makes the LCD last 25. Now in real life for a TV to make it through 5 years or more is a tough call. So practically speaking, even if the LCD lasts endlessly on paper, in real life it may not last that long especially with leaps in resolution and such.
Ghosmanas has a plasma and I don't think he would ever buy a TN LCD panel for TV viewing after it.