I can't see this being the case and am lead to believe that Google only allows one domain.com per keyword rather than only one domain.com/landingpageA, domain.com/landingpageB... and so on.
What about, for ex:
keyword: advertising
now we don't know if they want adwords or adsense, so advertising is both in the adsense and adwords campaign for two affiliates, one doing affiliate marketing for adsense and one for adwords.
one has www.google.com/adsense as landing and the other has adwords.google.com/ as the landing page.
If I was searching for advertising I would probably want both so I could choose better. But I'll onyl get the one that costs the most, not eh most relevant one, which is what google wants, right? Relevance...?
Maybe what should really happen is for the Google bot to visit our landing pages, making note of relevance between content and keyword. If this is high, and the bot finds not duplication in content on the domain, then perhaps this indicates that another ad serving the same domain would be okay.