The report claims that Google (and others) have been paying to be included on a "whitelist" that prevents blocking by the free browser extension.
Adblock Plus normally offers whitelisting for free to smaller websites under its Acceptable Ads whitelist, which states "unobtrusive ads should remain viewable as long as they aren't annoying."
In their FAQ, the company says "Managing this list requires significant effort on our side and this task cannot be completely taken over by volunteers. That's why we are being paid by some larger properties that serve nonintrusive advertisements."