The common adversary is the telecom industry. It’s an industry being undermined by the technological change of mobile computing and its profits are up for grabs. Apple and Google have different approaches in implementing this change but in the end they dismantle and absorb profits from the same target.
They are also benefiting each other. Apple benefits Google by creating user experience innovations which Google can rapidly copy. Google benefits Apple by increasing smartphone consumption–educating markets to the value of mobile computing and crippling the profitability (and thus the ability to innovate) of Apple’s direct competitors.