Yeah pretty much, you have to really research the model that you have, it can vary.
But the burn in happens because the avatars/icons/HUD are exposed in one location for a very long time. Look at a Wawa or 7-11 register display, or an old ATM display. BURN IN
How long does that take though, an hour, 3 hours, 7 hours? doesn't it take a real extended time, like days?
This will vary depending on brand, model, screen types. It's just a lot less an issue for newer systems
Without admitting exactly how long I can (and have) played Morrowind, I'll venture to say even a newer plasma isn't a chance I would take. :P We're happy with our huge, 150 lb tube right now.