Comment by bitwize

Oh God, it's as I feared.

Apple UI designer #1: Well, the flat design has been largely a success so far, but those darn users -- they can still easily pick out widgets from the background, and with a few tries still reasonably guess what they're for and how they'll respond!

Apple UI designer #2: I know! Let's make the widgets semitransparent. That way they'll be harder to pick out from the background, and Macs and iPhones will become delightfully fun puzzle boxes users will love trying to figure out, much like my dog loves his snuffle mat!