It's not exactly specific to the image preview code, but rather the code that handles the notification when receiving an iMessage.
The attack mentioned in the Wired article[1] relies on iMessage asking the sandboxless Springboard[2][3] to deserialize a maliciously crafted field, included in the incoming iMessage, to escape the sandbox. This specific vulnerability doesn't appear to apply to other apps.
It might be, it’s just that using Safari would turn a zero-click attack into a one-click one (click on my shady link). (Also, WebKit runs with a different sandbox that may require special effort to escape out of.)
