My understanding is that the knock sensor is still very much present, simply less sensitive than before. Running any motor without a knock sensor is an extraordinarily bad idea. Running no knock sensor on a modified motor with no tune, well, that's even worse.
A resistor is a very crude way of limiting the signal that the ECU sees from the Knock Sensor. Ideally you'd use a spectrum analyzer, and try to find at what frequencies the knock signal is most visible above the background noise (aka other shit banging around), and then apply some frequency selective filtering to further enhance the signal to noise ratio. Then accept only any signal over a set threshold as actual knock. While that sounds complicated and idealistic, it's also not needed when things are designed properly (sensor from Subaru) or when you add new variables to the equation, you compensate for them properly (tuning for your mods). Even with something like J&S Safeguard, a load qualifier is used to disable the knock detector under light engine loads and deceleration, where things like piston slap can cause an interfering signal. Remember: You are asking a circuit to detect knock that you can't quite hear, while ignoring engine noise that you can hear and the input is essentially a microphone. It takes real signal processing, not a $3.00 resistor from Radio Shack.
