What @Lightlyseared said, but this will probably change once streaming really takes off. That won’t be for a while yet, since studios, distribution companies, megasites like Amazon, etc. either develop or refine their streaming services. I expect the next few years to see a proliferation of streaming services as they battle it out to be the next Netflix. This is why Netflix tried to re-brand itself, to get ahead of the pack, but they handled it so ineptly they gave themselves a black eye.
Once the battle over streaming really kicks off, look for screen-to-home lag time to shift. Keep in mind though that the studios and distributors are trying to maximize their profits and find their footing in all this, so you’re probably not going to have instant film-on-demand for all titles for some time, if ever. You’ll need to be patient, regardless of how they finally determine how they’re going to provide content.