Using adwords, bloggers put up advertisements for companies they don't run, and affiliate advertising (which is the idea starting this thread) is similar.
I see what you mean though, that it would seem rude for BRK to make up their own ads for coke. At any rate, Buffett's approach is to not interfere in any of his businesses, so I'm sure that the two ads that are there (GEICO and Borsheims) would have been done in consultation. He could do that with coke etc, too.
I'm not saying he should do it, just that the same logic applies.
The point I'm making, tongue-in-cheek, is to echo Buffett's philosophy that when you buy a share in a company, you should think of it as buying that company, not as buying a share, so that you think of yourself as a business owner, and not a trader in shares.
Buffet does take every opportunity to promote his holdings, though you might argue that they're superior if he invested in them in the first place.