DTV on standard 4:3 TVs and CRT damage

[Jeffhs]

The laundromat in my town has a 23-25" Toshiba TV/VCR/DVD perched on top of a vending machine. I was there today doing my laundry, and noticed that the set was tuned to a football game; however, the picture did not fill the entire screen, due to the broadcast being in HD and this set being designed for the old NTSC 4:3 standard. This TV is left on from the time the laundromat opens until it closes--13 hours or so. My question is, will the CRT screen eventually be damaged from constantly showing an HD image with those black bars above and below the picture? I am also asking this for my own information, in case I have to replace my own flat screen with a CRT-based set. I have heard and read that it is indeed possible to burn the phosphors on the tube of an older CRT set by viewing HD images that do not fill the screen; in fact, I think I read here on VK of someone who had to junk an older set because of screen burn caused by extended viewing of HD content. Is this actually as much of a problem as it seems?