I thought I'd add my two pennies worth to this discussion. I'm an ex-helicopter and gyro-copter pilot, engineer, current glider pilot and now recent proud owner of a Phantom 3 (Pro), so feel I should know a little bit about this subject (VRS). Although the wiki explanation of VRS is sort of true, it isn't entirely accurate. VRS is the helicopter equivalent of a stall in a normal aircraft/glider, caused by the angle of attack of the in-flow being too high for the wing/rotor profile. In a helicopter this generally happens when demanding lift (i.e. increasing the collective/power) when in a fast vertical descending phase of the flight. Basically the rotor at the inner diameter starts to see high angles of attack, stalls in an erratic fashion, causing the bouncing around of the craft. Hence the 'descending under power' description. If DJI limit the downward speed of the Phantom, I can only think of one scenario that could cause VRS, and that is actually not in descending flight, oddly enough. If the quad gets suddenly caught in a strong upward thermal whilst actually attempting to descend (i.e. On minimum power / blade rotational speed) the rotors will see an upward flow of air through the blades causing them to stall, hence the VRS. Or coming out of a downdraft from again a thermal. Remember the quad doesn't have collective control of the rotor blades, or 'flapping' blades, as in helicopters, so it is more constrained.
The same corrective action applies though, get some forward speed on and the VRS will disappear. In the Robinson R22 the critical speed below which you need to be concerned about VRS is about 15-30kts, depending on rotor loading.