Yeah that's one of the issues with trying to build an anti-cheat in UnrealScript.  UnrealScript was designed for a specific purpose and that certainly wasn't to allow people to create anti-cheat mods.  You have to rely on pretty hacky methods to detect cheats.  dFb never got into UT2k4 but we did work on an anti-cheat project for a clan we were friendly with.  I have no idea how bad UT2k4 is now but it used to be pretty rampant with cheaters before we went to UT3.  But, as you said there is a much larger community of people that care and know enough to clean up the mess.