They haven't kept it open source, strictly speaking (ref. Honeycomb). Their naivety has left them dangerously exposed on patents, the recent CarrierIQ debacle is an example of the dangers of Android's openness, and any worthwhile app in the Android Market is hacked and re-submitted as a free app before you can blink an eye. Google's not making money from Android, and neither are developers*. That's not even starting on the security vulnerabilities, or the fact that Google's business model is based on a premise of invasive personal data-slurpage to sell more ads.

Granted, that's a generalization. But it makes the point.