[Grml] aptitude upgrade - lots kept back

I used grml2hd to install 2.16.15, and I've upgraded to 2.16.16.

Now when I run "aptitude upgrade", I have 259 packages kept back.

The following packages have been kept back: acpitool alsa-utils apachetop apcupsd-cgi apt apt-utils artwiz-cursor ... xprint-common xserver-xorg xterm xutils xvfb xvncviewer

I haven't modified /etc/apt/preferences. Have I done something else wrong, or is 259 packages kept back reasonable?

-- Tom White