HDTV is absolutely wonderful, not only are the images crisper and clearer, but we also see that part of the movie that used to be cut off when it aired on TV verses watching a movie at the theater on the big screen.
Although the picture size has gotten larger one thing hasn't change, and that's the title safe are of broadcast TV. The reason for is because although you might be watching the program on your 72" wide-screen, there are still standard definition TV in use, and if your graphics are out of the title safe area, then they don't fit inside standard definition. Please note that you must leave room for the stations bug on the screen in addition to your lower thirds fitting inside the title safe area.
When the graphics and lower thirds in your program you've prepared for broadcast television falls outside of these title safe areas, most likely it will be rejected by the station. One main reason for this is many people in the United States and around the world are still viewing television on standard definition TV sets. In fact although most people now have at least on HDTV, but rather than replacing all the functioning TVs in the house, which still work fine, they use them in bedrooms, kitchens, and dens, and they will continue to use them until they stop working. I am one of those mentioned people myself. I would like an HDTV in my bedroom, but my 25 inch standard definition TV is still working great, and I don't watch it very often; thus I can't justify replacing it at this time.
Below is a graphic that shows the title safe area inside a standard screen that is inside of a 720p screen that is inside of a 1080p screen. The title safe area remains the same for all files when aired on broadcast TV. Please remember Impact Media and http://closedcaptionservice.com for all your closed captioning.