I've been thinking about it and it just hit me. The reason why we won't see an App Store is an obvious one. It's not the complete package.
Why would Apple allow you to download apps to use on another companies television?
What would sell iTVs more than anything is to allow application development. This would also allow for easier development of the platform and Apple will not have to worry about the various third party screen resolutions.
Think about it, Apple would be...