If the stock would have otherwise been sold off like the others, then it's not really different because the price is higher now than it would have been.
E.g. Allegheny selling AAPL + Berkshire buying AAPL == Berkshire buying Allegheny
(Assuming a perfect market, which isn't the case but I don't feel qualified to say what the other effects would be)
E.g. Allegheny selling AAPL + Berkshire buying AAPL == Berkshire buying Allegheny (Assuming a perfect market, which isn't the case but I don't feel qualified to say what the other effects would be)