Jobs is a one of a kind visionary corporate leader, who sees the big picture and can define a course for Apple to remain innovative and profitable. Remember that the iPod was a loss maker when first introduced!
Now that's the good news for Apple. The bad news is that such leaders seldom leave any room for a second visionary leader in the wings. This type of leader demands creative freedom, to run with their ideas, without being second guessed all the time by someone with perhaps a divergent view of the future. Both may be valid visions, but two separate approaches can seldom coexist in corporate life, especially when producing cutting edge electronics.
Ergo the possibility of replacing Jobs with a new innovative leader from within the existing Apple structure isn't good. The next level is probably filled with more corporate talents, to round off Job's weaknesses, rather than visionary leaders "in waiting".
When Apple gets serious, about the eventual successor to Jobs, look for moves to buy smaller innovative companies with CEOs who want a bigger opportunity within a few years.
Just my 2 Cents.