That's normal. It's called overscan.
http://nicolep.digitalrice.com/tv/glossary.htm
I quote:
Overscan
The percentage of picture lost due to the horizontal and vertical edges being outside the viewable area of the TV screen. Overscan was introduced into sets to hide the fluctuation in picture size due to unstable voltage as well as to hide interference in broadcast material. Manufacturers conveniently use overscan when the quality of the extreme edges of the image is less than perfect. Most TVs come with an overscan setting of about 10%. The optimum is between 3% and 5% for watching material from a variety of sources.