Cumulative preferred stock buffers the risk of a skipped dividend payment by allowing past due dividends to accrue.

FORBES: Why Warren Buffett Prefers Preferred Stock

Non-cumulative preferred stock gives a company more flexibility in managing its cash flow.

FORBES: Why Warren Buffett Prefers Preferred Stock

As stated above, the preferred stock purchased by Berkshire Hathaway is cumulative.

FORBES: Why Warren Buffett Prefers Preferred Stock