Interesting. I would have guessed the opposite. I would think higher pressures would allow the tire sidewalls to deform less, so that handling would be tighter.
Traction, I would think goes down a little, since I would think the contact patch would be smaller, and generally traction goes up with a larger contact patch. On the other hand, the pounds per square inch of contact patch goes up, somewhat compensating for the smaller contact patch.
I wonder what the guys who track their cars do? Lower pressures at a drag strip for max traction, and higher pressures at Laguna Seca for max handling? Dunno.
The only thing I'd add, is when I feel like my car understeers too much when cornering, I add air to the fronts to increase traction. So, now I'm thoroughly confused.