A:  Because it’s as cheap as it’s ever been when measured using Buffett’s preferred valuation metric – Price-to-Owner Earnings*.

Buffett explains how he calculates owner earnings in his 1986 Berkshire Hathaway shareholder letter:

If we think through these questions, we can gain some insights about what may be called “owner earnings.” These represent (a) reported earnings plus (b) depreciation, depletion, amortization, and certain other non-cash charges… less ( c) the average annual amount of capitalized expenditures for plant and equipment, etc. that the business requires to fully maintain its long-term competitive position and its unit volume. (If the business requires additional working capital to maintain its competitive position and unit volume, the increment also should be included in ( c) . However, businesses following the LIFO inventory method usually do not require additional working capital if unit volume does not change.)

Our owner-earnings equation does not yield the deceptively precise figures provided by GAAP, since( c) must be a guess – and one sometimes very difficult to make. Despite this problem, we consider the owner earnings figure, not the GAAP figure, to be the relevant item for valuation purposes – both for investors in buying stocks and for managers in buying entire businesses. We agree with Keynes’s observation: “I would rather be vaguely right than precisely wrong.”

Apple is very cheap when compared to other famous Berkshire Hathaway investments.

For example, the price-to-owners earnings ratio of Coca Cola – one of Berkshire Hathaway’s largest stock holdings (14.43% as at 31/3/2016 according to the 13F filings of Berkshire Hathaway) is currently 26.4 times.

Apple is currently offers an attractive owner’s earnings yield of  11.5%, meanwhile Coca Cola’s owner’s earnings yield is a low 3.8%.

Not only is Apple significantly cheaper than Coca Cola, it’s historical revenue growth is more than 10 times as fast.

Apple is also significantly more profitable. It’s return on assets (RoA), or profitability ignoring the use of debt is 20.5% compared to 8.1% for Coca Cola.

* Charts courtesy of www.gurufocus.com