Well, I'm not sure; I'd have to program more in Smalltalk before I could say. But my guess is that it comes from the remarkable regularity of the language as well as, to quote Kay's definition of what he meant by OO, its "extreme late binding of all things" (I love that phrase!) These are the most interesting things about Smalltalk as well as the things that it has least in common with all the other languages called OO.
