The LBS I go to has a scale. All an enterprising prospective buyer has to do is put the bike on the scale to determine its weight.
I can see why the manufacturer's do not publish the weights. Different sizes of frames weigh different amounts. Also, the manufacturers buy their components and who knows when some process might change in the component fabrication that changes its weight? I would think if the manufacturers published the weight of various bikes it would be a warrenty that the bike weighs exactly that much and that could produce no end of head aches for the manufacturer. It is easier to make determination of the weight of the bike the responsibility of the buyer.