Help me understand these dependencies (xorg/video drivers)

[Matteo Riva <muradin@gmail.com>]

Debian testing installation. An aptitude dist-upgrade today results in:

The following packages have unmet dependencies:
  fglrx-driver: Conflicts: nvidia-glx but 195.36.24-4 is to be installed.
  xserver-xorg-core: Breaks: xserver-xorg-video-2 which is a virtual package.
                     Breaks: xserver-xorg-video-cyrix (<= 1:1.1.0-8)
but 1:1.1.0-8 is to be installed.
                     Breaks: xserver-xorg-video-nsc (<= 1:2.8.3-4) but
1:2.8.3-4 is to be installed.
  fglrx-glx: Conflicts: nvidia-glx but 195.36.24-4 is to be installed.
  nvidia-glx: Conflicts: fglrx-glx but 1:10-7-1 is to be installed.

but I can't understand why it's installing fglrx-driver or nvidia-glx

An aptitude why on those packages shows:

$ aptitude why fglrx-driver
i   gnome        Depends    gdm3 | gdm-themes
p   gdm3         Recommends xserver-xorg
p A xserver-xorg Depends    xserver-xorg-video-all | xserver-xorg-video-6
p   fglrx-driver Provides   xserver-xorg-video-6

aptitude why nvidia-glx
i   gnome        Depends    gdm3 | gdm-themes
p   gdm3         Recommends xserver-xorg
p A xserver-xorg Depends    xserver-xorg-video-all | xserver-xorg-video-6
p   nvidia-glx   Provides   xserver-xorg-video-6

so it seems they are installed since they provide 'xserver-xorg-video-6'
BUT I already have 'xserver-xorg-video-radeonhd' which provides the
same package, so why does aptitude want to install the proprietary
display drivers?

Also, can I safely remove every xserver-xorg-video-* except the one I'm
using?

Thanks.