Think object as if it cant draw itself, lets say you have a spreadsheet object that it can draw it self in some window manager so you are updating it with some method calls, etc and you want to share trough the network, what is the difference between serializing that object over the wire and drawing it in your screen than use some sort of json to wire the data and then recreate with a thin client the spreadsheet in your browser?

I mean the difference is subtle, you can say why we dont have the same draw engine and use json yo carry the data over the network? You will have to solve syncing, etc, but if you instead use something like a croquet (I'm assuming here, I don't have experience with that system) you are sharing the object, the methods the full object, not just a text representation of it.