I don't think you have it right. The buy-back doesn't make each share owned by the public worth more of Apple. What it does is makes the company own more of its own shares (i.e. more shares are owned privately instead of publicly). The easy way to understand it is to take it to the extreme. If Apple bought every share but one, that one shareholder would not own 100% of the company. If Apple bought every share that would be taking the company private.