I understand the reasons, and it may be great by comparison, but as an end user it's not really acceptable quite yet; people have to be able to use it to get something done and these little frustrations can easily push customers away.
To bring up my drive-thru example again, I mentioned it at the window and they said a lot of people were upset by the interaction too and had complained. Since there are alternatives nearby its easy to just not return to deal with "that".
Maybe some 'hold over' phrases could be used to fill the air while processing, like "sure, just a sec" , anything to let a user know that they were actually heard
