I can't speak for the other two systems compared, but to be clear, OP's examples involve more than "dictation and simple searches"; Siri also controls the device. Without entering the text messaging or email apps, one can tell the virtual secretary to read and write messages and emails. Assuming Siri understands your voice well enough.
Fun specific example at the lock screen after holding down the iPhone's button for a couple seconds: "Read the latest message from my wife to me." Then, still at the lock screen, "Reply to my wife I love you".
Maybe it's just my experience, but I did not care much for Siri until she allowed me greater control over my device. When she first came out, you could not ask her to read the screen; later, the program was able to toggle assisting configuration like VoiceOver by command.
Fun specific example at the lock screen after holding down the iPhone's button for a couple seconds: "Read the latest message from my wife to me." Then, still at the lock screen, "Reply to my wife I love you".
Maybe it's just my experience, but I did not care much for Siri until she allowed me greater control over my device. When she first came out, you could not ask her to read the screen; later, the program was able to toggle assisting configuration like VoiceOver by command.