The change was made since X has been able to set dpi to the correct value since XFree86 4.0 if you have DDC/EDID enabled. Pretty much all video cards and monitors made since ~ 1996 support EDID. If not you can still set DisplaySize which will cause it to compute the correct dpi. "100 dpi" is rarely the correct dpi. Now why gnome fonts are small I don't know since it uses fontconfig with libfreetype just like KDE does, so it should be able to deal with variable dpi just fine (afaik).
Chris
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