There is a difference between applying your core competencies to different markets, and just expanding. Apple has been good at limiting their growth to the form

There is a difference between applying your core competencies to different markets, and just expanding. Apple has been good at limiting their growth to the former. When they do expand into unfamiliar areas (like with iTunes), they make sure they contribute to the bottom line (through increased iPod/iPhone sales). There are already good Twitter applications for both the Mac and the iPhone. Apple gains nothing, and loses $700 million.