Will, those are great voices, but that stylistic approach, even though accepted as 'correct' in some folk circles, does not have a monopoly on greatness. There a lots of people who genuinely prefer the sound that Rachel, Becky and Lisa produce, and I honestly don't think it's a youth thing, or a fashion thing, or a marketing thing, or even a sex thing.
Some voices just come out differently, and some people simply feel more comfortable with a softer delivery. If the tuning and timing are fine (which they are), then the phrasing lies in the gift of the singer
There's a huge difference between "I prefer this" and "This is better."
Open-minds, open ears, open hearts. That's what's needed around here, specially in the 'season of good Will'