I have a 100Hz Sony Bravia 55incher that I bought in 2008 and it's still going strong. No dead pixels, no backlight imbalance, no errors etc.
However, I don't watch TV either passively or actively - there are more important things to fill my time with in my opinion and so I only use it for occasional film-watching. Maybe that's contributed to its' operational longevity. Dunno.
It's only LCD tech but the picture, with films at least is still absolutely stellar and gives a 'faithful' colour reproduction afaiac and I knw exactly how current OLED TV's look - I'm not overly impressed enough to upgrade any time soon. With live sports maybe there's benefits but for my level of use, forget it.
I saw something interesting on youtube regarding TV manufacturer built-in obsolesensce recently. I can't find the video back to link it unfortunately but essentially most modern TV's go into a shutdown error mode and shit their pants as soon as something trivial like a dead pixel or voltage drop on a lighting module occurs. There's a simple bypass that involves some soldering/re-wiring but he didn't show this for obvious reasons.
Another good reason not to upgrade anytime soon I think.
EDIT:
Here we go. Found the vid after dredging back through my watch history. I'll never get that time back
