I think you nailed it. They've been pushing hard on bringing the Google Cloud Services and App Engine up to speed, and if they can catch more big players early on, it will serve as good demos on how to scale with their systems.
There's a secondary goal here in that it benefits them to have a pool of skilled individuals out in the market who are familiar/expert on the Google platforms/technology.
So if they get a few hundred startups to use Google, most of them fail, a few hold steady, a few become heavy users of Google adn they make some money.
But - there's people from every one of those startups who now are familiar with how to use the Google platform and will potentially recommend/use Google at their next startup.
> vendor lock in.
I think this is the final goal
Nah, I don't think that's the final goal. Individually luring in startups doesn't scale well at all. I suspect they are trying to get a much higher 3rd-party throughput through their services to seed the community with use.
Also the emphasis on UX assistance and Play store priority sounds like they really want to improve the Android ecosystem.