Windows Phone 8 has a completely "flat" look too... I have my phone set to a white background (dark is generally the more common background) and zoned out a bit while refreshing a live feed.. when I got back to the page I thought I was looking at something for the new Windows Phone update coming in July. They're so extremely similar?!
The font and the phone answer screen are almost a direct copy. The lock screen is pretty similar too. EDIT: yes and the multitasking, I forgot that! I can't speak for other comparisons. Oh god I'm so not prepared to explain to ppl WP8 came out first when they say "pfft windows is copying apple". CNET rounded some up, there'll probably be more coming out this week though.
Familiarity of iOS7.
Not saying anything is wrong with that, they all inspire each other. But I'm putting the information out there.
I feel like we're taking a step backwards with these updates... I remember when you were completely able to modify the "themes" of your devices to make it almost unrecognizable... and now we get the courtesy of one "theme" update and it's played off as the phone being reinvented.