Finally i could understand what http://brainstorm.ubuntu.com/idea/14179/
When installing Ubuntu, all partitions and disks are not recognized to be writed at '/etc/fstab', which we have to set them by hand. @TalAshkenazi has the point, it's not easy for newbies.
This should be easier to be supported, and as well a tool can help us to edit easily '/etc/fstab' when replacing disks would be welcome as well.
The coders also must not forget there are tons of disk system formats beyond ext, ntfs and fat, like hfsplus, nfs, xfs, zfs, reiserfs, etc.
Also not to forget is the fact of old versions of RedHat (before Fedora) used to do this by default... Why is this so missing on Ubuntu, from 4.10 to 8.10, is a complete mistery...