In a panic stop on dry pavement it's virtually impossible to actually lock the wheel with standard braking systems (including non-ABS) -- the decelerative force simply exceeds the tire's grip capacity. You may think the wheel is completely locked but it's actually still rotating. You lose a lot of rubber, but it's lost somewhat evenly around the whole tire. When the tire is hydroplaning though it's quite easy to completely lock the wheel and it will remain locked (particularly if there's some level of rubber reversion going on -- melting or melted rubber) when the car exits the plane, thus almost instant pop.
I can see the logic in that. Thanks for the explanation.