While I don't know if they do, I can see why Google might prioritize review of accounts which are about to receive a payout over ones where that's far in the future: once the money is sent, it's generally not recoverable. That's when Google has the highest quotient of [data on the account] * [value at risk], so that's when it makes sense to review.

AdWords and AdSense policies tell advertisers and publishers that advertiser spending on evicted publishers are refunded for the preceding 60 days. Because this policy has to do with revenue recognition, it's presumably under SOX control, so it would be difficult and very risky to willfully violate it.

So Google faces a larger cash loss if they cancel a publisher just after a payout than if they do so before. And they have no incentive to cancel publishers just to keep the money: they refund the advertisers, so they lose not only their share of the advertising spend, but they have to pay the publisher share of any unrecoverable previous payout out of their own pockets.

Disclosure: I used to work for Google.