My only reason I can come up with about why Smack Down is more accurate than rock throw is that either...
A:The stone is bigger
B:The stone is thrown so fast that the floating/flying Pokemon wouldn't have time to dodge.

My other thoughts is...
How the hell is is a physical move if "The user throws a stone or projectile to attack an opponent."
Does that still make is physical?

That's my thoughts on Smack Down for now, so thanks for reading.