The Weather app had been powered by Yahoo! previously so they could have partnered with them after the release of their app to do the default app and update it for iOS7.
It has a big yahoo icon in the corner so I'd say yes they did this.
That's exactly how I feel; good description sir!
Re:iOS 7, thoroughly reviewed
by shawndumas on Wednesday September 18, 2013 @03:24PM
(#6407437)
it looks the same because Yahoo built both.
Before it was 100% obvious what the icons meant at a glance -- a big yellow unmistakable sun, clear full clouds, etc.
The new ones are just outlines, you almost can't tell the white and yellow lines apart, you have to "decipher" them with your eyes to figure out the weather for the next few days. A huge step backwards in clarity.