Well, you can divide most display technologies into two systems - the imaging system and the light engine. The screen will fail when one of those two systems fails first.

The N900 screen is like an LED TV, it uses an LCD panel (TFT) to make the image and an array of white LEDs to make light.

LCDs are very robust (provided you don't crack it). You can completely melt a digital watch in an oven and the LCD will still work. The LED backlight would be the limiting factor - except they used multiple LEDs. So even if one fails, the others will still illuminate the screen.

This is not true of the AMOLED screens used on HTC phones. Organic screens have a shorter lifespan. (AMOLEDs ues less power, so they sacrifice long-term display life for short-term battery life.)

I buy Nokia because of their hardware. Not only the most feature-packed, but also incredibly rugged. I leave my screen on when charging because I use my phone as an alarm clock. Because it's TFT LCD with LED backlight, I have no hesitation about doing so.

Say it shortened the life of the display from 10 years to 8 years. Do you think you will still be using your N900 in 2018?