Why can't I use my webcam with all my contacts I chat with?

[Mand]

I have successfully used my webcam with another Yahoo person, however my friends that do not have a yahoo account I am not able to select them when I try to turn on my webcam for chat sessions. Why is that. I can chat with them ok, but it doesnt show them as an option for anything else. I have also tried inviting them to view my webcam but they dont appear to receive any such request on their end. Is this purely because they are with a different chat application to Windows