I see what you mean, but I think it's just a matter of them continuing to refine the visual effects shots in the time between the teaser and the trailer. I first really realized this was common practice when I noticed this change between the Edward Norton Incredible Hulk teaser and a TV spot from a couple months later:

Aside from flipping the ship for the shot (the new composition is much stronger, imo), the new Prometheus trailer likely has much greater lighting, texture, and atmospheric detail than the earlier renders used in the teaser. I'm sure if you compare other shots, you'll find more improvements in the CGI.