OK, here's my answer to your question. Note that this is for the USA only. I've no idea how it's done elsewhere.
1. Movies that you rip from DVDs or BluRays will not be available for iTunes in the Cloud streaming on the aTV or Mac/PC. To watch these movies on an aTV2/3, you would have to have them loaded onto a Mac/PC with HomeShare enabled.
2. Movies that you purchase from iTunes will typically be loaded onto your iTunes library on your Mac/PC. Streaming from the Mac/PC to the aTV2/3 will work. Also, some movies are available for streaming via iTunes in the Cloud. I don't know the ratio, but there are many movies on iTunes that are not available via the Cloud.
3. If a movie is available for streaming over the Cloud, I think it's also available for streaming the Digital Copy (obtained through the purchase of a BD or DVD combo pack). Of course the Digital Copy is available to stream via Mac/PC as well.
Perfect. Thank you!