Ah yeah, I love old DDL. He makes other actors who think putting on 60lbs for a part means they're committed to it, actually look ambivalent about their work. His methods and whatever aren't so interesting to me, as the result. All the extremities he goes to, as you list them there, are surely extraordinary but I also think you used a great word for him too: he's eccentric. These methods only work because he's a genius - not every actor who commits to his level would get the same results.
There's an exactness about DDL when he acts, it's as if he gets the part in all accuracy - but even the small things he does, the grimaces, the sideways glances, the blank stares, they all become bigger and more compelling. He's magnetic in ways few actors are, maybe because we're aware of what he's done to achieve this level of virtuoso, so we lean back in glory in it. He's signaled it all in advance, through on-set anecdotes and his own marvelous record of achievements.
Sometimes I think of the advice Laurence Olivier gave to Dustin Hoffman, when Hoffman said he was going to stay up all night before filming a scene, so he'd look suitable jittery and jaded: "Why don't you just try acting, old dear?" But of course, there are many ways to skin a rabbit, and DDL's way gets incredible results.
Here's an outtake from the great film you watched:
[video=youtube]http://www.youtube.com/watch?v=yjNw3pNsSmM[/video]