I think the difference is that the "traffic acquisition" mentioned is direction of people to Google Search, like the Mozilla partnership, and not to specific search results.
My iPhone browser has a google search field, and I am sure that Google pays for that, and that it drives traffic to its ads. It is money to drive traffic, but doesn't mess with Page Ranking.
Afterthought: Also, not only does that mozilla stuff work as traffic acquisition, it's also branding. So there's some other value for Google there.