Google is expensive
Ignoring for a moment that Apple only does acquisitions with prices with an 'm' in them and not a 'b', they'd be far better off buying Nokia. Nokia's mapping software is from all accounts superior to Google's, they have a much larger cache of mobile patents, and fewer businesses they'd have to sell off or close. More importantly, it'd cost a fraction of what Google would.
I mean c'mon, I could maybe see Apple keeping search if they owned Google, but they'd have no interest in running all the stuff like Mail, Apps, Shopping, Google+ and the dozens of others. Apple likes to specifically target on particular businesses, while Google is willing to try anything and see if it works. It'd be like Exxon buying P&G.