I don't think that Mark is saying that he is buying shares cheaply.
I think he means that Buffett can use his reputation and huge cash to buy shares below the prices which the rest of us would have to pay.
Let's say for some reason, Irish public companies in general were prepared to sell shares to me at 20% below the prices available to others, then I would expect to beat the average.
Obviously, it's smart for Buffett to get himself into that position.
The other unusual feature of Buffett is that, for some years, he has been buying whole companies, rather than just buying shares. He does seem to have an uncanny ability to buy large, profitable companies cheaply.
Brendan