Booting and login - why are users not logged in automatically?

[Asif Youssuff]

Was just playing with the latest daily-live cd (testdrive is very
cool!) and noticed that when installing, after entering a username and
password, the "Require my password to log in" is selected.

If the ureadahead daemon is optimized for auto-login ("slightly
assumes you're using auto-login; so waits about 45s after the display
manager starts before it stops reprofiling" from
http://ubuntuforums.org/showthread.php?t=1434502), why is this the
default option? Shouldn't the fastest boot be the one that is
preselected, especially if the ureadahead daemon is optimized for this
use case?

-Asif