Ultimately though, Facetime doesn't do anything which ichat doesn't in terms of functionality. When you look at it, it's actually more complicated technically as it has to connect via a regular voice transmission before opening wifi. This means that, for example, the ipod touch won't be able to use facetime if it gets a camera in September.
Apple haven't done anything revolutionary here - its just that you can be assured that it 'just works' with the iphone.
I don't think skype will need the 'videochat API' (if there even is one) because all they actually need is access to the camera. It then is just a case of streaming that data to another skype user using the skype protocol. If skype bring video chat to the iphone, it will be completely data based.
Makes me wonder if either Apple will update iOS4 at some point to include just data calling, or if skype will be politely asked by Apple not to develop a video chat option (or implement it using the facetime open standard).
Personally, I like the idea of facetime, because it means I can have ONE contact number to allow me to connect with everyone. I'm fed up of having half my friends on ichat and half on Skype.