Apple already has a Hulu Plus app up and running on Apple TV but may be delaying its launch due to concerns it will compete with iTunes TV Show sales, according to 9to5Mac. Their sources claim the Hulu Plus for Apple TV is now feature complete and ready for release, and has supposedly been ready for release for over a month. The reason for the hold is thought to be political and not related to any technical issues.
While Apple TV 2 has had Netflix since launch, their content is mainly older, catalog shows, not the new releases that are more profitable for iTunes.
Hulu Plus is already available on iOS, and in HD on a few other set top boxes such as the Roku and the Western Digital TV Live. It would make so much sense to have it available on the Apple TV too.