Trek and Specialized don't make most of the bike. They make the frame, and maybe other minor parts like the saddle. The rest of the bike (the vast majority in terms of weight) is made by other companies- Shimano, Easton, etc. Trek/Specialized can't control or guarantee the weights of all these components so they can't give you a total bike weight.
Component manufacturers are notoriously optimistic about their weights. It's normal to be 10% or so off.
If you want the weight of a specific model, the only reliable thing you can do is either go to the LBS and throw the model in question on some scales. Or ask someone else with the same bike to weigh theirs.