According to various sources, Apple has the final build of Hulu Plus ready to go but they are holding it back not for technical reasons, but for political reasons as they are worried that the inclusion and availability of Hulu Plus could hurt their iTunes Store sales, since Hulu Plus offers similar content to the iTunes Store.
At the moment the Netflix and iTunes Store combo is working out for Apple, with Netflix offering older content, while iTunes offers up fresher content. Should Apple release Hulu Plus for Apple TV, those with Hulu Plus subscriptions on other iOS devices may stop visiting the iTunes Store as often, or even stop visiting completely.