I think that having their own mobile os lets them keep the status quo. If apple changed google for bing, even when a lot of people would change back to google search, i bet that a big percentage would simply use the default (think about ie8). Also, it lets them refine and make more relevant their search results, collect geodata for other services (transit for example), expand their services, etc. its not like th
ey are mother theresa. And above all, it helps them expand their core business, letting every device maker use a smartphone os that doesnt suck, all with google as default search engine.
