I'd also like to point out that not every religion has even similar beliefs about what's respectful. For example, I'm Wiccan. Technically, if I'd wanted to, I could have gotten married wearing nothing but a smile and my new wedding ring (aka "skyclad"), and been perfectly respectful in terms of my religion. I didn't do that for many reasons...but it would have been a valid choice. So I think it's important to consider the couple's religious traditions/beliefs, among other things.
Every bride should abide by what's considered appropriate for the venue and her personal/family beliefs around such issues. So long as she does so, I don't think it's fair or correct to consider her "disrespectful". It's fine to say "I personally wouldn't be comfortable doing that," but making a blanket statement that it's disrespectful does come across as judgemental.
For the record, my actual wedding dress was a Renaissance-style dress; it showed a bit of cleavage, but nothing extreme, and had full sleeves. But it wasn't a traditional wedding dress in the modern sense - it was in shades of green with gold-colored trim. So was I disrespectful for choosing a "nontraditional" style and color? Even though green is associated with fertility, the Earth, and lots of other positive things by many Wiccans and other pagans?