Why don't we get hot pixels while using live view mode, but do get then on a long exposure? I read somewhere that they appear due to the sensor being activated for too much time, but then, live view should also show them.
On a long exposure charge is allowed to accumulate on the sensor over a period of time, whereas in live view the sensor is discharged for every frame (so thirty times a second or so). Some hot pixels result from slow charge leakage which only occurs during a long exposure, hence you wouldn't expect to see these in live view.
Also liveview subsamples the sensor so you dont see every pixel.