Android is based on the Linux kernel. User-land is not required to be open-source. Dalvik, Android's SDK, all user-land libraries, the whole of open-source Android is not required to be open-source. You may notice that the license is Apache 2.0, a license that's incompatible with GPL v.2 ;-)
> What is the line from Android to Bing? Does google open source google? gmail?
The line is that Bing is not core to Microsoft, but complementary, so why not open-source the technology behind it?
In fact, Bing is even less important for Microsoft, than Android is to Google, because Android for Google is their insurance that they'll stay relevant in this mobiles connected world. Without Android, Google would be at the mercy of the various walled gardens that popped into existence, a trend started by Apple ... quick question, can you set Google as your search provider on Windows Phone? Maybe you can, but I can't do it on my Nokia Lumia. There is no way to make that search button open Google and the option in IExplorer doesn't work.
Open-sourcing Bing would be great for everybody, including Microsoft, just like when Yahoo open-sourced Hadoop. Yet, they won't do it - because they are the same bastards, that's why.