Isn't the fact that Wayne saves his life also an important beat?

Totally agreed, Scot. Reese's threat to reveal Batman forces the Joker's hand. The threat of Batman's exposure causes the Joker to recognize just how much he needs Batman as his nemesis--and thus in the world. "I had a vision. Of the world without Batman....And it was boring." The Joker sets up the perfect dilemma for Batman: will he (or anyone) kill Reese, thus saving a hospital full of people? That Batman saves Reese, his enemy, is yet another twist of moral luck--and irony--in the Joker's devilish deadly game of chance.

@Scot Boyd: That's actually part of that third section of the Reese subplot I was referring to, and as DAF notes slots right into Reese as Trickster: Tests Wayne to see what he'll do, forcing him to save this little asshole who would threaten to first extort money from him, then reveal his secret identity, and bigger picture take Wayne - and everybody else's - eyes off the ball allowing the Joker to chill with Harvey Dent.

I'm with @Scot Boyd.

There's the culmination beat -- which is Bruce Wayne (not Batman) saves his life.

Right @James. I had typed Wayne and then lost the post and had to rewrite it and mistakenly put in Batman. For me, @James it heightened the irony that it is Wayne--not to mention the way it happens. Or did you see something else in the fact that it's Wayne not Batman? @Scott, if this is a test, is Wayne passing or failing?

@DAF: I'd say Wayne passes the test, especially if you look at the theme of violence as a central one to the story -- Wayne / Batman's pledge about the proper use of violence (set up in Batman Begins) vs. Joker who keeps trying to get Batman to break his pledge. Here he saves Reese from an act of violence that could potentially kill him (the other driver hell bent on crashing into the police van with Reese inside). But in passing that test, it sets up for a Final Struggle between Protagonist vs. Nemesis: Batman vs. Joker.

That's often the case with Tricksters, their tests lay the groundwork for the Final Struggle.