Ubuntu likely simply inherits that behavior from Debian. I don't use Ubuntu much, but I use Debian all the time. Debian's grub2 install by default uses UUID. I have found that this is generally highly desirable compared to the bad old way of doing things. It's especially useful when dealing with USB drives and BIOS hard drive boot priority...those things can really mess with the drive enumeration. By using UUID, all that's necessary is to boot from the desired hard drive (whether by setting the BIOS boot priority or selecting via a boot menu).