The X server can't figure out what the resolution of a monitor is if the
DisplaySize parameter isn't set in XF86Config. When it has to guess, it
usually guesses 75dpi instead of 100dpi, which (a) is questionable given
the high resolution of most modern monitors and (b) makes fonts and such
look really awful.
The database used by Xconfigurator should have monitor sizes and add them
automatically to the generated XF86Config. For database entries that don't
have a monitor size, Xconfigurator should prompt for it.
IMHO users should never ever _have_ to configure something like this.
It should be autodetected wherever possible, and default to something
minimally sane elsewhere. Forcing DPI setting, or even presenting
it somewhere by default is an overcomplexity IMHO that a user shouldn't
need to see.
It is however questionable wether 75dpi is a sane default or not. It
is the X server itself which chooses 75dpi however. Basically DDC probe
sets the DPI. If DDCprobe fails, or if a user supplies DPI info, then
the commandline or config file take precedance.
Not sure if this belongs in the X config tool or not right now, but
I don't have a 100% hard opinion on it yet either. Plus X has changed
quite a bit since this was filed, and X will be changing even more
yet to come.
I'll reassign this to redhat-config-xfree86 for now.
redat-config-xfree86 allows you to set the DPI (display size), and it defaults
to using what DDC probes.