Question 3a: Why is there a perceived change in location for both tones? (i.e. why is the perception different for ILD than for ITD?)
Question 3b: Why is this demonstration very artificial?
Humans are sensitive to ILDs at all frequencies. ILDs do not depend on phase locking but only on the overall level of activity in the auditory nerve.
However, in reality, a single sound source with a frequency of 500 Hz does not create a significant ILD for humans because the wavelength of the sound is much larger than the diameter of the head and, thus, the sound passes around the head without significant attenuation or reflection.
This figure shows the ILD vs. frequency function for two humans:
(from Usher and Martens, 2007)