I've had several accounts banned while babysitting, responding to every chat, doing under 6 hours a day, etc. Jagex does indeed have detection systems in place, I have even seen people get banned within minutes of starting their bots. The fact of the matter is that Jagex does have the capabilities to record your mouse movements and decompile them and prove that you are botting. The only bots I've ever seen that is fully undetectable is Robotz In Disguise. The programmer there has graduated with a programming and mathematics degree in a very reputable university. He has replicated human mouse movements, and following these Guidelines ->
http://www.robotzindisguise.com/Guidelines.htm not a single person has been banned while using RiD since they were formed in August 2008. Only 21 people have been banned breaking the Guidelines in that same time. That's an estimated 0.0007% ban rate split across all of their bots.
TL;DR version:
Reflection and BCEL scripts are detectable because they have decompilable mouse movements, and other things that give Jagex the proof they need to ban you.