Also, if you just want someone to stare at you while you blather on, how do you know they're listening?
Kidding. I see your point, being interupted is annoying. It doesn't mean they're not listening; it really, really doesn't. It's just that they're bubbling over with thoughts from what you've said already and how can you move on in the conversation if you haven't cleared up this part yet?
Sometimes, if you know you need to get to a certain point before they will know enough to contribute, you can tell them: "wait until I finish, because this is important".
You have to respect someone elses approach in order to get respect for yours. (And part of respecting someone elses approach is actually not expecting them to do it your way )