No, of course not. I video iChat with my wife all the time. Of course, she has a Mac too.
I haven't tested aMSN yet for chatting with other MSN users, mostly because the only other person I know who uses MSN (other than myself for testing with my now-webcam equipped Dell) and is equipped with a webcam is someone I dislike talking to in person, much less on a dedicated video chat.
I do sort of wish video equipped AIM users could video chat with iSight equipped iSight users, but oh well.
Oh, I sent my parents my old non-iSight equipped Mac Mini. Then I bought a Rocketfish USB webcam for them. I had them download iChatUSB, and indeed that worked just fine with that USB cam, and iChat. This way I don't have to call them on the phone. When they call for technical support I can tell them to point the camera at whatever is vexing them and be better able to fix whatever technical issue of the week comes up.
Oh, and you can make silly little
videos when you're bored. ;D