I believe they rate difficulty mostly based on the man made features. So a mandatory drop or gap automatically is rated pretty high on difficulty. Gotta think about all the less hardcore mtb'ers that rent a demo bike for the day.
The di%khead factor is so high with this. If one of these guys rode out in front of me and I hit them. I would kick them while they were on the ground for damaging my car.
HELLS YES! It takes so much skill to casually ride on wet concrete like that, any park rider will attest that it's damn near riding on ice when wet for most skate parks.