doesn't vegas have motion tracking?

No. Vegas has Track Motion, which is different than Motion Tracking. Track motion allows you to move the entire image within the preview space. Motion Tracking allows you to identify specific vector points within the image and follow those vector points.
For example, say you had an eye over which you composited eyeglasses. As the subject moves their head, the eye moves in position, and you'd like the glasses to follow suit. Rather than keyframing each move, motion tracking simply follows the eye, causing the glasses to move along with the pixels contained in the eye.
Not the best explanation, but hopefully it explains the difference.

so Vegas doesn't have motion tracking then (in the eyeglass sense). it doesn't matter what happens in the preview, it's the final results that are more important.

to me this is a great thread. it is too bad that vegas is split between HD and DV forums. You really need to look at both forums - very confusing.