Licurg: This might only be an impression, but I think TBS games usually have less hacking in them. At least, I don't recall ever meeting a hacker playing one of them.
Turn based games require patience, which something 95% of cheaters, especially the younger ones simply dont posses.
Then ofcourse, many turn based games are far more pure skill based, when autoaims and such simply do not help. So for those who just want to cheat and ruin other people's games, fps and mmo are simply more easy than forexample Go is all about skill, not slightest sliver of chance and where all the moves are visible to both players.
Blood Bowl has dice, but as far as I know those are on the server and you cant touch em.
Thinking about TB's the most obvious thing to cheat at would be visibility, in games like civilization - not sure if that can be made though. Stuff like cheating resources or so would propably we visible post game atleast, if the game supports playback - like many TB's do -> quick ban for the cheater.
Anyways, TB's are often take far more seriously by the players than FPS's as in FPS its easy to just change server - but to a TB you often have to invest far more time, atleast if the game involves more than 2 players (civ type games for example).