I believe it is due to the different operating systems and rules used by them to govern the connections between the two devices, some of these rules may be mandated by the specifications for USB.
Be thankful the Ipad does NOT drain the battery like an Android device. Many people HATE the Android drain and if you do a google I think you will find many complaints about it. I am awaiting the arrival of a 5S iphone bought to run the fly app but NOT suck the controller's battery dry, the Samsung S6 bought for use with the App does a grand job but drains the controller's battery
That said I have also read that some android devices can switch off the charging but I can not guarantee that that is correct etc.