I think it's also neat how what Sam said at the end of this episode connects back with the bit in 6.01 where he said "Because you care, and that's who you are. Me? I wouldn't even think to try." He knows even then he should care, and there's something wrong that keeps him from caring like he should (and like he used to).

And I think you're exactly right, about the fight at the end. I know the anger has to be part of it, but something I was commenting to kros_21 this morning was that even when he has finally blown up in the past, it's always been just one punch. The absolute beat down, yeah, that just has to be so Dean can incapacitate Sam.