They would fix any doubt if they began releasing bugs and exploits for Android as well.
They do offer a bug bounty for their own products, to encourage third parties to do to them exactly what they're doing to Apple and Microsoft.
Of course, it's an uphill battle with the manufacturers/carriers. But as long as Google is not applying fixes to Jelly Bean, the manufacturers can always blame Google.
[1] http://www.androidpolice.com/2015/01/23/google-issues-offici...
[2] https://developer.android.com/about/dashboards/index.html