And you already know this, but it's not actually "money" until the shares are
sold.
The nuance here that the MR peanut gallery exaggerates, but that you seem to completely sidestep - is that Icahn is not likely in this for the long term. Just as there may have been stock price benefits with all his tweeting today, there will be consequences when he goes to cash in on the raised share price after his proposed buy-back.
I am a shareholder, and I have made money from AAPL. But I do not support Icahn's motives of making money - at least,
not in the way that he proposes. The value of my shares tripled long before any dividend or buy-back program, and I'm fine with that. Icahn wants to profit, at the possible expense of others - perhaps many of us. Not interested. He has no fiduciary responsibilities to me like the Apple Board does, and if Apple is damaged after he is liquidated, I'm sure he could care less. So, while his motives are understandable and completely legal - surely you can comprehend why I distrust his manipulative behavior, to the extent that it may impact me outside of my best interests.
As to the scale of Apple's cash hoard, you are totally correct that I (and most people) can't even begin to fathom it. But I also can't fathom what Apple could do in the next 20 years. When it comes to Mars, iColony has a nice ring to it, actually.