You would also think that Rockstar would want to stop those kinds of cheats just for greedy reasons. If there is some kind of ultra-powerful flying saucer item available, it's probably something that they sell to players for money. At the very least, when someone spawns something like that, check to see if their account purchased it.

So much of the rest of the stuff could be handled using heuristics. The average player gets X headshots an hour, this player is in the 99.9th percentile. Maybe they're just very good, but let's flag that account and see if there's anything else suspicious about their playing. That's the thing about an MMO, you have vast amounts of data about players so there's a lot of stuff you can use to see if something is normal.

I guess if they're not doing it they've done some business calculations and decided that investing $X in techniques to ban cheaters won't result in at least $X more in revenue from happy players who want to play more now that the cheating has been reduced. I wouldn't be surprised if they're counting on making money off the cheaters somehow -- maybe they periodically do get detected and banned and have to buy a new copy of the game. So, the math now says you don't want to be too aggressive about the cheaters because they're a good, reliable source of revenue.