It is also how Harden drives. When he drives he presents the ball out in front of him, enticing defenders to swat at it, then he moves the ball, drawing contact on his arms getting an easy and obvious call. LeBron is more traditional in that he tucks the ball into his body, lowers his head/shoulders on a drive proctecting the ball. So most of the contact against Harden is obvious hacks, and most of the contact on James is harder to officiate body contact.
Harden is one of the best I have ever seen in enticing defenders to foul him, because the ball is such an open target on his drives.
This. James knocks people back with his shoulder more than MJ/Kobe ever did...and a lot of those are fouls. But part of that is LeBron is a physical force who can get to the rim like that on anybody. MJ/Kobe got fouled slashing or posting up.