I'd also like to add that I've been botting a skill non-stop for a week now. I'm trying to get 120, and I've been using the bot since level 1. ATM @ 50m XP.
Personally I believe they do monitor accounts, I believe they run most clients on test servers and monitor the clients for hours/days until they build a pattern on a very large scale. They give a set value, then monitor all new accounts, and accounts that have just been logged in for a set period of time. Jagex is a huge company with millions in sales. I believe they attribute a certain score based on xp/mouse movement/activity and run that score to certain tiers. Each time your score sticks out you move up a tier and each tier lasts a preset number of in game hours. As you move up in tiers your looked at closer. I do not believe they log every single byte of data. I think they just give you a score based value related to how you have played the game i think the values are constantly changing and the values are based on the gaming community as a whole. I think the values are then regularly changed based on events to get a new baseline. I think they have more then one form of detection tho. I think they have a built in client validator that could dramatically effect your score. Missed mouse clicks, and efficiency over time. Most players when fighting monsters will have a monster ready to attack after the current dies.Clients have a day as they do not see the monster dead until it vanishes. They see the most users make a mouse movement within 0.25 seconds of the monsters health bar to drop to 0 yet clients wait a full 1-1.5 seconds until the monster vanishes. I think its a collective whole rather then 1 fine tuned system that looks at bock like activity. I think they also record some users game play to look back and watch to see if its a bot client. I'm not a expert on bots but I feel I'm a good judge when it comes to noticing bots.
