Black Bars. What's the deal?

I have a 55 inch Mitsubishi wide screen rear projection t.v. I own over 100 DVD movies and most of them are in 2.35 aspect ratio. When I play them I have top and bottom black bars on the screen. When I play the DVD's with 1.85 aspect ratio it fills the entire screen. In my t.v. owners manual it has a page warning you not to leave stationary or letterbox images on screen for an extended period of time and that uneven picture tube aging is not covered by my warranty. Example of these are letterbox top and bottom black bars, sidebar images, stock-market report bars, shopping channel logos & pricing displays, video game patterns and scoreboards, bright station logos and on-line internet web sites. I have been using my zoom function on my DVD player to fill the entire screen when using a 2.35 aspect ratio DVD. A fellow at my local audio video store told me that the black bars at the top and bottom can not burn a lasting image on my screen and when I use my zoom functiion to fill the screen it degrades the picture quality of the DVD. My question is: Will the black bars ruin my t.v or not? Any comments will be greatly appreciated. Thanks in advance.