Apple & Google are competing and they are trying to outdo each other. What resulted is more advanced phones and cheaper prices. Consumers win.
Can you imagine if nobody challenges Facebook? Did you know that what Facebook released recently (better Photos, messages, etc) is a preemptive response to Google+?
We have seen time and time again that monopolies are bad. Internet Explorer did not innovate for some time when it was in 80+ of computers. Microsoft started paying attention to IE again when Firefox and Chrome came out.