ok this might be difficult for you to understand. there IS a difference. when you talk at something, it is as if it you are talking to an object that isnt human and its like your not having a conversation, it is just the speaker talking. we sometiems use this as a joke when someone does not listen. example: "she just kept talking at me and wouldnt shut up" the person saying this would be a little annoyed. when we say talking ABOUT someone, you are refering to something or someone, and the topic is related to it.

You can talk to someone about something. You can talk about anything to someone. You do not talk AT something. If it is not a person, it won't hear you. You can talk TO a person or to an animal that has ears and can hear you.

I don't really get it. What do you think talk at something should mean? I think you talk about something to someone at some place. So I talk about the weather, to you, at the train station.