I don't agree that gaining control of the user account is that much smaller of a concern then root access. You can do a lot on a Mac with just the user account. And then, local exploits providing privilege escalation are relatively common.
There's no advantage really, though, since the gksu style authentication popup system when you need admin privileges is very painless. I too doubt if many people run their Macs as root.
$ sudo passwd
Changing password for root.
New password:
Retype new password:
passwd: Unable to change the password for record root. Credential verification failed because account is disabled.
$