You are both right. You CAN edit grub.conf manually, but it is not the best
method because if you update the kernel it will overwrite your manual
editting so it is wasted effort. A better method is to have Ubuntu
update-grub. If your purpose is to remove older kernels then you should use
apt/Synaptic to do that first. After doing this it will automatically edit
grub. If you want to change a settings such as the time the that grub is
displayed or change the default OS then there are utilities for that. If you
are old school then you can edit grub.conf, so long as you know that your
changes can be undone and you may have to repeat your work.

The trend in Ubuntu is to move away from old school and dumb things down.
For people with the skills they can always work around this using the
commandline and tried and true methods. As Steve pointed out grub2 is quite
a bit more complex. It supposedly loads faster and that is the name of the
game when many distros spend inordinate time and effort to shave a second
off boot time and sites such as Phoronix compare distro boots head to head.
Editting grub manually is not something people should do unless they have
the skills. One mis-type and you can be in for a big headache. That is why
it is recommended to leave it up to the system to manage it. However, for
those who like to live on the edge there is nothing to stop you.

The forums are full of horror stories of things that can go wrong. People
need to know the consequences of their actions if they make a mistake. So it
should be done with caution. When you edit grub manually if all goes well
then you are ahead of the curve. When things go wrong you may have to use
the Live CD to undo the damage. Experienced users are not put off by this,
but newbies are.