While it's gotten rid of the worst spam (apps sending totally unrelated ads as notifications), unfortunately there are holes in that policy big enough to still drive a busload of junk notifications through, as long as they're somehow related to the app:

> Apps and their ads must not display advertisements through system level notifications on the user’s device, unless the notifications derive from an integral feature provided by the installed app. (e.g., an airline app that notifies users of special deals, or a game that notifies users of in-game promotions).

To me those are still pretty spammy. An airline app notifying me that a flight I have a ticket for is delayed would be one thing; that's a legitimate use of system-level notifications. But an airline app vibrating my phone, just to announce that AirlineName Has Great Deals To The Caribbean In Our End Of Summer Sale? That is not ok, but Google allows it. I assume this is also how Yelp is able to send that kind of junk notification without getting banned.