Security risks?

[neuhoff at mhccorp.com (neuhoff at mhccorp.com)]

Having created a live Debian for a USB stick with 'make-live' using among 
others the '--username  usblive' option I noticed that the USB stick always 
boots into the 'usblive' user account. And any command which require root 
privileges are to be preceded by the 'sudo'.

Questions: 
Is this really a secure setup?
Why doesn't 'sudo' prompt for a root password?
How exactly was it configured so as not to even  prompt for a password for the 
normal user after bootup?
And how exactly was it configured so as not to have a root account? 

Is all the magic done via the /etc/sudoers file only?

J.Neuhoff