xgl server and nvidia GPU

Why xgl server seems to disable direct rendering ?

I made an apt-get upgrade on 07/03/2008 on a Gutsy and it corrupted my xserver setup.
So I ran a glxinfo and direct rendering was no more.

name of display: :1.0 <-- why 1.0 and not 0.0, even if I have only 1 xserver session started !!!
display: :1 screen: 0
direct rendering: No (If you want to find out why, try setting LIBGL_DEBUG=verbose) <--- not very useful since I never get any verbose messages
server glx vendor string: SGI <-- what on earth is that !!!
server glx version string: 1.2
server glx extensions:
    GLX_ARB_multisample, GLX_EXT_visual_info, GLX_EXT_visual_rating,
    GLX_EXT_import_context, GLX_EXT_texture_from_pixmap, GLX_OML_swap_method,
    GLX_SGI_make_current_read, GLX_SGIS_multisample, GLX_SGIX_hyperpipe,
    GLX_SGIX_swap_barrier, GLX_SGIX_fbconfig
client glx vendor string: SGI
...
OpenGL vendor string: NVIDIA Corporation
OpenGL renderer string: GeForce4 Ti 4200/AGP/SSE/3DNOW!
OpenGL version string: 1.5.8 NVIDIA 96.31 <-- huh ??
...
 visual x bf lv rg d st colorbuffer ax dp st accumbuffer ms cav
   id dep cl sp sz l ci b ro r g b a bf th cl r g b a ns b eat
  ----------------------------------------------------------------------
  0x2c 24 tc 0 32 0 r y . 8 8 8 8 0 24 8 0 0 0 0 0 0 None
  0x2d 24 tc 0 32 0 r . . 8 8 8 8 0 0 0 0 0 0 0 0 0 None
  0x2e 32 tc 0 32 0 r y . 8 8 8 8 0 24 8 0 0 0 0 0 0 Ncon
  0x2f 32 tc 0 32 0 r . . 8 8 8 8 0 0 0 0 0 0 0 0 0 Ncon <-- only 4 visuals ??

I scratched my head, began to panic, re/install my legacy Nvidia proprietary driver many times with
no probing results. I was very puzzled since OpenGL acceleration was still there
but direct rendering has disappeared.

Finally, I get some hints on Ubuntu launchpad and I removed the xserver-glx.

Once removed, the glxinfo spitted out correct report :

name of display: :0.0 <-- good
display: :0 screen: 0
direct rendering: Yes <-- ahhhh, at last !
server glx vendor string: NVIDIA Corporation <-- yeeehah !!
server glx version string: 1.4
...
OpenGL vendor string: NVIDIA Corporation <-- ok
...
and a lot of visuals <-- me happy now

Strange isn't it ?

Is there any problem with xserver-glx and Nvidia ?
Does xserver-glx implicitely disables direct rendering ?
Should I trust glxinfo ?

Nop