Gdm was installed by the Debian installer. What I do not know is whether the Debian installer uses apt (I presume so, but I do not know).
You know that the Debian installer gives you the option to install some package sets. I presume that gdm belonged to the "Desktop" set. David > Was it automatically installed? If you're unable to answer that question, > this > may be closed as a non-bug. > >
