If my calculator is not mistaken you should get no gap. Have you double checked all your settings in track motion, project settings etc? Do you get the gap in preview, in render or both? How big is it? Is it only horizontal? Could it be down to the interlacing being unmatched between the different events?
Tor
Many cameras do not record the full 720 width. For example, my Canon XL-1 has about a 4 pixel black area on each side of the picture. You may simply be seeing that area (assuming a vertical black line from top to bottom.
You CAN get around this. Use Pan/Crop to crop the edges of the video and then use Track Motion to size and position them.