I think this is because iphone has never allowed background apps to hold open persistent connections, yet android does but with device and power-state specific

I think this is because iphone has never allowed background apps to hold open persistent connections, yet android does but with device and power-state specific limitations. So the iphone version of any xmpp app has to use apples notification service, but the android version of the same app might try to use a direct connection (saving the app developer a lot of server costs), even though on many models of phone it only works when the device is charging for example.