As I have not had the pleasure yet of burning onto DVD I wonder if it is in fact true that only the "Safe Areas" will show up on the TV screen?
Why such a differance between TV and computer?
The safe areas are an estimate; they vary greatly from one TV to the next. Older televisions usually had much smaller safe areas than newer televisions do now. Then again, as a television ages, the image shrinks so the safe area becomes bigger. My television at home shows almost the entire top of the frame, but cuts off quite a bit of the bottom (maybe my picture tube has "settled" in the case). So, the safe area borders in Vegas are just a general guide to help you plan for the worse.
A computer screen is intended to show the entire usable area of the frame. You wouldn't want the menu at the top of the screen or the scroll bars to be hidden behind the bezel around the screen. Televisions have an image larger than can be seen so that you don't see the rough edges caused by the analog transmission signal around the edge of the picture.
I would plan for a future where the viewer will be able to see the entire image that you see on your preview window in Vegas. This is what the DVD players running on PCs show right now; it's the conventional TVs that overscan and thus hide the perimeter of your image. It's for this reason that you still need to use a smaller center area when planning your action and titles. I predict TVs of the future will not overscan at all, or will have an adjustable overscan feature.