I did not cut Lee's arm off. I just knew Lee wasn't going to make it out of the story (no, I did not know how the end would go), so I figured it'd be a little easier with two hands.
I dunno if this happens in the version where you do cut it off, but Lee will have occasional blackouts. One while climbing the ladder with Kenny and almost falling.
I sent Lee across the sign first and when he goes into zombie-chopping mode, with the bitten arm he picks up a broken shard of glass as his second weapon (although Lee performs no double-kills, unfortunately). He even looks at the bite on his wrist and squeezes the glass shard in anger until it cuts his hand.
In my version of the game, Clem shoots and kills the stranger after Lee has a scuffle with him. I was pretty shocked by that, considering that makes sweet little Clementine a murderer.
He has another blackout with Clementine when she sees her folks in the horde they're trying to sneak through and Clem somehow gets him into the room where the game ends. I dunno if this happens differently if you cut off Lee's arm.
And I think what's happening with Clem after the credits is that she is totally uncertain as to whether or not she should go check out the people on the hill. It's the total inner conflict of deciding whether or not to reach out to the figures as they could be friends, enemies or walkers...
It reminds me a greatly of the decision The Boy has to make at the end of The Road