> But when he buys, he either buys all of a company, or enough of it to have some level of control over it, and that's only possible these days if you're wealthy as he is.

A lot of that is simply that he now has too much money to be able to efficiently buy bits of companies. His early career was still based on value investing, but mainly consisted of regular stock purchases. Berkshire Hathaway still has decent-sized chunks of Coca Cola and various other companies on its books.