1. You can disable automatic login from System --> Administration --> Login Window --> tab Security and uncheck the "Enable Automatic Login" check-box.
2. There are valid reasons why Ubuntu developers did not permit root login. I admit it is really annoying to digit your password every time you use sudo for administrative commands, but take in mind that you can stick with your system administrator's privileges for an entire shell session if you use the command:
every subsequent command will be run as if it was preceded by sudo and you have not to type your password again and again.