Stupid stupid stupid. If I have my IOS device with me why would I log into icloud? So were creating a system that only works when you don't need it?
Just because you don't log in doesn't mean others don't, and if someone were to try and compromise your account anyways they would use iCloud.com to gain access since they don't have access to your iPhone.
This isn't stupid, this is the right step into preventing all of the social engineering that surrounds the security issues of today. Social engineering is more common place now a days than any other type of "hacking."