Buffett is running an investment company. The day Berkshire Hathaway can't do a better job of earning long term returns than it's shareholders can, is the day it no longer justifies it's existence.

There have certainly been times where Buffett has struggled to find good investments, and in the short run a dividend might have seemed wise. But those times always pass and letting cash pile up until opportunities arise has worked very well for him.

Apple isn't an investment company. They are a consumer products company. Their new product ideas should not require large amounts of capital. Even the silly car idea should never get more than $10B or so in funding until it's proven, which is mice nuts in their grand scheme.

So they should return excess capital to shareholders. The only limiting test is how much is 'excess'. Tim Cook is likely being very conservative, but in the future if Apple has to ride out some bad years, having a hundred billion or so in the bank might prove the difference between success and failure.