Well, if you're sceptical Crab and Nick Lappos has dispelled the idea, then perhaps I'll be revising my thoughts there anon. But they currently go something like this:
In presenting a lower friction surface, asphalt will give a better inflow to the rotor and result in a bigger angle of attack for the same pitch position. The effect may not have time to develop, given rate of descent, flare height, the rapid transition from flare to settling and pulling pitch. But if there is a floating element to the end of the auto, I would hazard it could make its presence felt and help mitigate a bad outcome. A marginal aid to help save the day.
When trying to land with rotton right TR problems, more ground effect from asphalt will reduce the power requirement, and a lower pitch position is clearly more of what you want as you look for the right constellation to run on.
TT