The backlights for LCDs can be replaced, but not by the normal user.
30,000 hours is a long time actually. I have been using computers since 1981, and in that time have had approximately 11 different monitors, and 4 notebooks with TFT LCD displays.
If you run your computer 8 hours a day, that is 3750 days of continuous use. That equates to over 10 years. The longest I have ever kept any monitor is about 4-5 years.
What this says is that those folks who like to keep their systems on 24/7, it would be prudent for them to simply turn the LCDs off when they are not actually using them.
Notebook LCD displays do not last forever. They are subject to backlight failure anytime after about 5 years of use.