To watch movies are just stupid. Who would want to watch a BR movie on a computer. Most people have big TVs with surround. Watch it on that.
iTunes has a movie store, for purchase or rental.
Do you think NOBODY watches any of that content on a computer?
I'm sure the actual numbers of people who use Apple TV are tiny. Even Steve Jobs called it "a hobby" not a business.
That means the bulk of people are watching on iDevices, which are far more inappropriate than a computer given their screen sizes than a computer would be.
Or, another way to look at it - it's fine to watch a movie on a 9.7" iPad but not on an 11" Macbook Air?