Here’s what I wrote in response:
Two reasons come to mind as to why most developers don’t do this:
- Doing the Game Center integration, with Apple’s UI, is less work. That approach “wins” when money is tight. Many games are developed on the rockbottom development budgets, so this sort of additional feature is hard to justify especially given the potential trade for additional actual game content. Leaderboards, achievements, etc. are typically (and incorrectly) viewed as outside of core gameplay.
- There’s no direct API to “rate” an app, but you can on Apple’s provided Game Center UI. In an App Store where ratings (and to a lessor extent Facebook Likes) are currency of enormous value. Anything that may potentially reduce the likelihood of getting even a single rating is not viewed… favorably.
Until the second issue changes, the first argument won’t even happen because, in most cases, it’d be pointless. The elegance will come once the iOS SDK has the APIs, and only for the most resourced teams (initially.)
Bonus issue: This isn’t that easy to do. Look at your screenshot – there’s at least one critical bug (overlapping text in two places) and, IMO, there needs to be a blur layer or something to make the text more legible because there’s not enough contrast between it and the clouds.