Cowboys and Aliens is a film about "cowboys" in the 19th century fighting off an alien invasion in a town in Arizona. The cowboys and indians theme is so passe and politically incorrect these days, which is probably why the producers of this film opted to go for the far-out story angle - using aliens instead of Native Americans as the bad guys. In fact, in this movie, the Arizona natives help the cowboys out a bit.
Cowboys and Aliens presents extreme contrasts, with 19th century technology against super advanced weapons of destruction from outer space. What can a lowly cowboy do against an alien fighter ship that's got an arsenal of ray guns and grapplers that snag people up into its belly? In the movie, actor Daniel Craig's character has the answer attached to his wrist. It looks like a fancy flashlight, but it's got a secret. But, that's not what this post is all about. It's about the cables used by the aliens in kidnapping people. Why no use tractor beams?
In Cowboys and Aliens, there are scenes where the alien ships kidnap people at random. The victims are lifted up, or rather pulled up, into the air by what appears to be a cable. The cables appear to be those used in movie stunts where a harness is used to support the stunt person or actor, but in the trailer of Cowboys and Aliens, it would seem that the cables are part of the technology used by the aliens. It's strange that cables are used when those aliens are supposed to have technology that gives them command of gravity. The tractor beam is reasonably the better choice. But the producers of Cowboys and Aliens probably opted to use cables instead of optical effects to give the alien ships a more industrial "feel." If that's not the answer, it could be that the special effects people only forgot to digitally remove the cables during post production. =)
Cowboys and Aliens also stars Harrison Ford as a grumpy sheriff-like figure.