I think the trend towards minimalist closets has encouraged people to limit their personal color palettes. I think a lot of bloggers and others get caught up in the "perfect black pants, perfect white shirt" sort of quests, and end up with a whole wardrobe full of black and white.
Also, it's become more acceptable for women to be "uniform" dressers, and I think for many this leads to a limited palette, regardless of where they fall on the classic/edgy spectrum.
Also, pattern mixing, which has become pretty big in pinterest-land etc, is a lot easier with fewer colors -- or maybe people are more excited about pattern mixing because they're wearing less color?
Also, I see a lot of looks that rely on a lower-investment piece for a color pop, such as scarf, belt, cami, etc. So maybe there is an economic element -- people don't want to invest in a color they may not love for long? or that may be "over" by next season?
I'd agree with Angie that any color can be polished or RATE depending on the wearer and the context, and same goes for prints and materials. We've reached an era where even denim is not inherently rough or casual anymore -- and it certainly isn't as edgy as it was 50 years ago!