I do not mean to be defending Bd's customer service reps or anything like that - I just think that their fabric choice is a reasonable one. No tent is perfect, and everybody has different features or design variations, including fabric choices, that appeal to them for the uses they put the tent to - which is good, since that gets us a variety of tents to choose from. The people at BD aren't saints or devils, they're just businesspeople, trying to make a buck like everybody else. Sure their choice is based on money in the end - they are making the choices they think will sell the most tents. If it costs more to make, they'll charge more for it - and maybe that will mean they sell less of them. Or mayboe not. Are they right or are they wrong? I don't know. I think they make it clear that those tents need to be seam-sealed, and as long as they do that it seems like a valid choice, as opposed to a basic quality issue.
As to weight, I did a little calculation:
First, I'm assuming that if they used a PU coating on their silnylon so they could tape it, they'd use a coating similar to what MSR uses on their fabrics. I have previously figured out pretty carefully the fabric area of my Twin Peaks (don't ask), and I know from research prior to buying it that it is very, very close in size and configuration to the BD betalight. Based on that info, the weight difference is just over .38 oz/sq yd, which would give a total difference of 2.5 oz for the coating - and some small additional amount for the tape.
To me that would be worth saving - I mean, I'd rather seal it myself and save a couple ounces and a few bucks. Now, some would say that they'd rather get the added water resistance of the PU coating, and the reduced slipperiness perhaps, and that might be worth the added weight to them, but I think that's a whole different discussion.
I guess what I'm really saying is that it seems harsh to rant on them for a valid design decision as if it was a deceptive practice. I think the two are very different, and deserve different treatment. That's all.