If the person you spoke to on the phone had made themselves clearer they would have been doing a better job. The silnylon fabric BD uses on their floors can't be seam sealed using tape like a PU coated fabric can (see Franco's post) So their two options are to use a coated fabric (which was what the person you talked to on the phone was trying and failing to get across, that they have to use a silnylon fabic that also has a coating of PU - making it heavier - before they can tape the seams)or to hand-seal the seams the same way you would do it at home. As has been pointed out, this is a deal-breaker for a big manufacturer. I think it's a reasonable choice for them to do it this way, but the guy on the phone did a poor job of explaining it.
So in other words, the weight he's talking about saving is not just the weight of the seam sealer like you would apply, but of the added coating on the fabric that would allow them to tape the seams. I have an MSR twin peaks made with silnylon fabric that has the added coating (and taped seams) and it weighs 4-5 ounces more than a Betalight (almost identical size and shape) that uses regular silnylon without the PU coating. so the weight differnce is meaningful.