It's not the goal of Windows Phone to be like Android.
Letting other services onto the phone doesn't get people using Microsoft's services.
They could make a requirement of loading a browser on the phone that it has to default to bing.
This move would increase developer interest probably.
Most people I know who use smartphones (Android) uses the default Browser (not even Chrome)
I thought the recent Android phones have all defaulted to Chrome for the browser? Or is it just the Nexus devices that do this?