Difference between root login and passwordless sudo

Honestly, this is probably largely an attempt to protect the user against themselves. One of the biggest benefits of "don't run as root" is that mistakes don't (usually) destroy the whole system. (On desktops, this is of limited value -- I'd rather destroy my Apache configuration than all the data in my home directory!) If you are using ec2-user, you at least need to realize you're escalating privileges by using sudo. In that way, it is similar to UAC on Windows for an Administrative account.