You make some good points and I was pretty much pulling those figures out of the air (I didn't mention a time period!), but loosely basing them on this article I had read on Asymco,
http://www.asymco.com/2013/04/04/the-cost-of-building-galaxies-and-iphones/:
"In 2012 Samsung spent around $20 billion while Apple spent about $10 billion (excluding leasehold improvements or Apple stores but including real estate)."
Also, bear in mind that Apple has already promised to return $100b to shareholders by Apr 2015
http://www.apple.com/pr/library/2013/04/23Apple-More-than-Doubles-Capital-Return-Program.html , which by my calculations is pretty much all its cash currently on book after a reduction for future tax liabilities.
But that is not enough for Icahn, he wants it all and he wants it now!
Here's a black swan event where $50b might come in handy. What if there was a catastrophic seismic event in California, similar say to the tsunami in Japan. Say Apple's production was crippled for two years (like Marvell in Thailand after the floods a couple of years ago, or Canon in Japan after the tsunami), maybe personnel affected, Californian economy takes a big hit, US economy takes a hit, iPhone sales drop sharply, stock hits $200/share. Meanwhile Samsung, Xiaomi and Lenovo are doing just fine. That would be a great time to buy shares back
and have enough money to rebuild operations as quickly as possible
and donate money to local causes.
I'm not saying now is not a good time to buy shares (quite the opposite, I'm a buyer), and their last bond issuance was a very well-timed move. But $100b is already an enormous return of capital, and frankly Icahn gives me the creeps.
Here's another scenario which is even more likely. What if 10y rates, against all expectations, actually start to head back down and this 5 year bull market morphs into a 2 year bear market? Then you will have borrowed money above par, your stock will still not go up because of the weak market, and you won't have a war chest at the bottom of the market when it is most useful.