Although the author is the creator of the Dark Sky app himself, he does point over several strong design points why it works better on iOS widget over Yahoo weather.
The only change is the addition of the “Open in Dark Sky” button, and the italicized text. The button serves two roles: 1) Obviously it provides quick access to Dark Sky for more information. And 2) it serves as a visual clue (along with the italics) that something is up. This makes checking the widget fast and painless: Pull down the notification center, is there a button? Nope? You’re good to go.
He made a lot of sense.
Keeping things simple. In my opinion, text is still the best form of communication through iOS widget. You have no need for images, especially when the space over at the widget area is limited