I think the frame material only changes the bike weight by a couple of pounds, its the components that are the differences making the difference in bike weights. A lower price bike will generally have heavier equipment attached to the frame.

I think that if you compared bikes of different materials, that have similar equipment that the weights would be within a few pounds. I think that if you want a great steel frame that it will cost you a similar price as high end carbon. frame.

I am surprised that you found a steel frame to compare with carbon or aluminum. My LBS wouldn't have steel frames laying around unless they are really old.