I think it's the backgrounds everywhere that make iOS 7 look so busy, especially the home screen. The screens that are simple text-on-background or boxes-on-background look fine, and the chatbox retains a pure simple white background.
In cases where the white background exists, the stylistic similarities to WP7/8 look more obvious. WP7/8 make very limited use of elaborate backgrounds, preferring to go with jet-black. There's an option to invert the WP7 colors and go with black text on white background... it makes iOS7 look like a complete clone there.
I was on the Montréal metro this weekend and really like the flat design they use which WP8 really took to heart. It will be interesting to see if the way iOS does it leads to more confusion for users or if skeuomorphism was the way to go.