iOS does tell you have to turn it off but the user has to notice a small notice on the Spotlight control panel. Same with OS X. I believe this kind is unethical as Apple knows that most people won't change the default settings.
Yes but also the privacy implications are over exaggerated. This kind of "phoning home", at least for Apple Siri/Spotlight, goes through a session ID which is random, regenerated every 30 minutes, and not bound to Apple ID or other user profile. Moreover, IP addresses are not used, not communicated to third parties (eg: Bing for Siri) and anonymized in logs. So yes, it's a "phoning home", but with different implications compared to eg. inputting a wifi password on a logged-in Android phone.
There is nothing unethical about it. It would be if there was no way to turn it off.
The default setting should be to respect the privacy of the user first. Since they know most users will blindly go with the default, it's an asshole play.