I had to go look at my other models of that size: the Hot Wheels and Johnny Lighting ones. You can't see a curve on those, so I went to the mag that came with it. If you look on page 16, the top part is curved, but if you look at the one right on the next page (17), the bottom is curved.
Is it the viewing angle?
Perhaps. According to these images from TWOK, it's angled at the top and bottom, but I guess the top seems a little more pronounced.
http://movies.trekcore.com/gallery/albums/twok/ch7/twok0582.jpg
http://movies.trekcore.com/gallery/albums/twok/ch12/twok0912.jpg
http://movies.trekcore.com/gallery/albums/twok/ch13/twok1040.jpg