Before Google Play Services, updates were a big concern for Android. If Android N had the feature you wanted, but Verizon/Motorola only shipped N-1 for your Droid, you were out of luck. There were pie charts routinely tossed around showing which devices had which Android version numbers. You don't hear those concerns nearly as often anymore.
Makes me wonder what the tradeoffs/alternatives are. Maybe they could have still moved features to a Play Services-esque library but published the source for it. Considering we're commenting on a post about how developing in the open is too inconvenient for modern Google, the difference might have been moot.