Perhaps the change is for exactly the reasons he cites:
First, Berkshire has gradually morphed from a company whose assets are concentrated in marketable stocks into one whose major value resides in operating businesses. Charlie and I expect that reshaping to continue in an irregular manner. Second, while our equity holdings are valued at market prices, accounting rules require our collection of operating companies to be included in book value at an amount far below their current value, a mismark that has grown in recent years. Third, it is likely that – over time – Berkshire will be a significant repurchaser of its shares, transactions that will take place at prices above book value but below our estimate of intrinsic value. The math of such purchases is simple: Each transaction makes per-share intrinsic value go up, while per-share book value goes down. That combination causes the book-value scorecard to become increasingly out of touch with economic reality.
Maybe the third reason should have been listed first. Take a look at the equity of a company that buys back stock on a regular basis. Moody’s is an extreme example, at 12/31/17 the MCO had negative equity of $114.9m.
I see this as a clear indicator that major stock buybacks are coming soon.