Any product not fully machined from metal is going to have a tolerance value on how much it weighs. A little extra glue, the seat rails cut slightly long, a little extra foam or the density slightly high - anything like this and you'll see a slightly higher weight and that's normal.

I'm all for weight-weenie-ing (you should see my MTB; it is 7 lbs lighter than when I bought it) but there has to be some management of expectations when it comes to built-up parts and their expected weights.

DG