Most trailers these days for big, big shit like this show numerous alternate takes, extended takes or deleted footage in the promotional build. Prometheus is no different.
I do think it was cut to the quick, but not too much to visibly hurt beyond a somewhat brisk opening arrival at 223. I was expecting something much more jagged in the second hour based on commentary online, but I think it cuts very well. Most of the complaints before tonight hinged on the fallout or lack thereof of Shaw containing the squid-baby in cryo freeze in the pod, but having seen it, I thought that explained itself - she froze it, neutralized it, they got it and they need to go see the Engineer - and absolutely no one in the theater gave a shit.