I see. 2 hours isn't THAT short, dude. They could pull an AVP and make it 90 minutes.
Remember, Avatar had James Cameron, the beginning of the 3-D craze, and, well some other stuff I won't mention. Prometheus has Ridley Scott, yes, but his name isn't as automatic as Cameron(in the public eyes). And the 3-D might help it, but this isn't being released at the beginning of the current 3-D craze, its coming at the end.