I think in Berkshire case they do, as they are swimming in cash and notoriously don't sell unless their business outlook changes dramatically.

In any case, I would not take what Berkshire does with much weight.

As Buffett himself said, if you took out their 5/6 best performing investments out of their equation they would be matching the sp500, and if you took out 20, they would be trailing it.

They know that their over performance came from a small number of incredibly well performing bets.