You realize, I hope, that Icahn is speaking publicly like this to try to force Apple to increase the buyback.
He is not a friend to Apple. Icahn has purchased a billion dollars worth of Apple stock. He wants the value of that stock to increase by some significant percentage (20%, 50%) very quickly, so he can sell it and make a buck. If things don't go his way, he'll do anything to Apple to force the issue. That's how he operates. He's not about creating long-term value or companies that are healthy over the long term.
By publicly creating the hope and expectation of a bigger buyback, he increases pressure on Apple to make a bigger buyback, whether or not that's fundamentally good for the company. Icahn creates the possibility of shareholder discontent in the absence of an increased buyback.
the problem with the stock buyback is how Apple will do it. Effectively because of high taxes to spend overseas money in the USA, Apple is going to "borrow" the money from a US bank, purchase the shares on the US market, then have the overseas operations pony up money so "Apple USA" doesn't have a "loss" on the books.
Guys like Icahn are just a little too greedy and not cautious of RISK when doing something like this. They see the easy money, but they don't pay the price when it takes years to clean up the mess. Part of Apple's stock position includes their cash in the bank.. so if they spend the cash... to BORROW money, they can get screwed over pretty quickly because their remaining stock price will automatically drop $100 just to cover the spend down of cash. then they have to account for lack of new products and an "adjustment" if new products hiccup... Tim can dig a hole pretty quickly where suddenly Apple has to actually "pay for stuff" when a month ago they were living off interest.