Why can ubuntu dist upgrade dist from within an X session?

[Πρεκατές Αλέξανδρος <aprekates@gmail.com>]

In release notes it says:

"You should not upgrade using telnet, rlogin, rsh, or from an X session 
managed by xdm, gdm or kdm etc. on the machine you are upgrading. That is 
because each of those services may well be terminated during the upgrade, 
which can result in an inaccessible system that is only half-upgraded. Use of 
the GNOME application update-manager is strongly discouraged for upgrades to 
new releases, as this tool relies on the desktop session remaining active. "|

So i wonder why can ubuntu dist upgrade dist from within an X session?


aprekates