>> Why, for instance, do class methods rely on annotations?

Python do not have annotations. Decorators are not like java annotations.

>>Why not take advantage of the explicit self?

I think "self" is good. Python lets you bloody patch python objects and classes in runtime and "self" makes it more clear.

Something like:

class MyClass(object): pass

def setX(self,x): self.x = x

MyClass.setX = setX

mc = MyClass()

mc.getX = lambda self: self.x

(INB4: I do not think that bloody patching is good practice)