There is no way they are going to release an app for the iPhone or iPod touch, if they did, they would have to deal with the fact that both devices have significantly lower resolution, there is no way to comfortably watch a movie on such a small screen, keep in mind that most, if not all movies are designed for larger screens.
Try reading text on a page shown in a movie on a screen the size of an iPhone. Try seeing that guy in the background or just far away, without higher resolution, you wont be able to recognize that guy, the list can go on and on and quite frankly, it's obvious, there's a reason we watch movies with high resolution TVs, this device is probably the lowest resolution that Netflix is willing to support, they also have to consider the overall customer satisfaction, which I'm sure would be reduced if they released it for small devices.
On a side note, the iPad and iPhone use pretty much the same software, if they really wanted it on both devices, I'm fairly certain it would have been done at the same time.
The resolution of an SD TV is no higher than the resolution of an iPhone. Try watching a clip of a movie from youtube. It's not as nice as watching on a big screen TV, but it works. Remember the iPhone is a lot closer to you than a TV that is across the living room.