I confirm that this bug is still present with Mesa 11.0.6.
Without forcing "DefaultDepth" to 16, I get:
$ glxgears
libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: r300
libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: swrast
I confirm that this bug is still present with Mesa 11.0.6.
Without forcing "DefaultDepth" to 16, I get:
$ glxgears
libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: r300
libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: swrast