Because it is more abstract it is more powerful. The notion of an object implies persistence over some finite time and the potential of indefinite persistence.
Objects are autonomous.
The object receiving a message is responsible for invoking the correct process or rejecting the message. This implies dynamic typing. From the sender's viewpoint the type of object receiving the message may be only partially determined and may change dynamically. The Object Oriented User Interface OOUI is a method of incorporating the object view of the world into the construction of a user interface. By narrowing the cognitive gap between the design and the implementation it tries to simplify the process of constructing the interface.