It would seem to me that they could easily add the weight to the geometry specs...
So, no question about size and weight. Add a weight for each of the XS, S, M, L, & XL bikes.
Specify exactly what components are weight, and which ones aren't.
For me, I'd weigh everything from pedals to seat (one will eventually have to choose a seat). Leave out bottle cages if one wishes to save a half an ounce.
If it is a touring bike that comes with a rack, weigh that too, or provide a separate weight with and without the rack.
Yeah, I can imagine some users going online and screaming bloody murder because of a 1 gram discrepancy.
One can list bikes, say 100 grams heavy, and fewer people will scream and holler if their bike is 100 grams lighter than specs.
Personally, at least in the road bike world, I think manufacturers know that high end racing bikes are hitting 14 to 15 pounds, and they don't want to put their 20+ pound bikes next to the 14 pound racers.
The same thing is probably true in the MTB world. Do you really want a 20 lb MTB? Is it rugged enough?