You are deffinately not alone. There are several other children out there who do the same thing. A good friend of mine is a speech therapist and sees this alot. They give it the name 'palilia' among others if it is something more extreme or there are other behaviors that go along with it. If you are really concerned you can talk to your Dr about it, they most generally reffer you to a specialist to just check it out. Also, most children do not even know they are doing this. I was told that you are not to keep point it out, that may actually make the child do it more often.
I personally don't see any connection to him playing in his room by himself talking to the toys...but that's just me.