I'm with you, sad to see no SDK and App Store on the ATV, I think they're really missing a great opportunity to make that little box something quite powerful, but they must have their reasons.
I do expect at some point to see an ATV app store, but when? Just because no app store or SDK this WWDC doesn't necessarily mean it won't happen before the next WWDC (he said wishfully, and definitely naively), right?
A reason to be optimistic - they announced with iOS 7 support for 3rd party game controllers. This is a first step toward gaming on the ATV...