HBO plays a bigger role than you might imagine in Apple’s negotiations with Hollywood to offer recent movies via the iTunes Store and its new iCloud service to devices such as the iPhone and iPad. HBO’s deals with studios including Warner, Fox, and Universal give it the exclusive right to digitally distribute their films during the premium TV window. (Others such as Starz have similar rights.) That’s been an issue for the new UltraViolet cloud initiative backed by most major studios and consumer electronics companies. Except Disney and Apple: UltraViolet is designed to reinvigorate home video sales by giving people who buy certain DVDs and Blu-ray discs the right to access their movies from the Internet cloud.

Warner Bros had to restructure its deal with corporate cousin HBO to clear the way for this week’s first UltraViolet release, Horrible Bosses. But Apple’s now talking to studios to secure the right to offer movies at the iTunes Store that can be accessed via the iCloud service — which was launched on Wednesday. That poses two challenges to Time Warner: The company has lot invested in UltraViolet as it reintroduces its web site Flixster as a user-friendly gateway for films stored in those digital lockers. And HBO is making a big push to promote its HBO Go digital streaming service. So keep an eye on Time Warner and HBO: The fate of their initiatives, as well as iCloud, will be shaped by the positions they take as Apple and other studios talk.