I have been selling projo's for some years now and my best explanation is this, the tubes in a projection TV are usually about 7" in diameter, they have to be a higher intensity than a regular tube tv to give an adequate brightness for the screen size, so to answer your question, it is not so much that regular TV's cannot get burn-in but it is more likely on a projo. My best suggestion is just make sure you turn down your brightness and contrast settings as much as you can and try not to play too much of one particular game if you suspect it might have graphics that will cause burn-in.

P.S. do not rely on built in screen savers in DVD players to prevent burn-in, most will not kick in on the interactive menus and you can still get burn-in on from the text.
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