There was much talk after Jump The Shark about Sam being so like John. And yes the whole "revenged obsessed, driven by guilt that I couldn't save the person I loved and in the process disconnecting from everyone in my life" parallels are striking. But one thing we must remember when looking at how Sam's character is that he was raised by both John -- and Dean.
Dean: I was six or seven, and he took me shooting for the first time. You know, bottles on a fence, that kind of thing. I bulls-eyed every one of them. He gave me this smile, like... I don't know.
I imagine this scene is bittersweet on two levels for blurryinthebackground Dean. It must remind him of those times with John, when he did feel John was proud of him. And maybe too, I think, times when he did this with Sam, wanting Sam to be part of this thing he loved. Moments when it was perfect, and other times when Sam pushed him away.
Dean: Y'know, I finally get why you and Dad butted heads so much. You two are practically the same person. I mean, I worshiped the guy, I dressed like him, I acted like him. I listened to the same music. But you are more like him than I will ever be. And I see that now.
Sam: I'll take that as a compliment.
Dean: You take it any way you want.
It's not only that Dean doesn't want Sam to be like John with the obsessive revenge shit, it's that Dean now feels with Sam like he did with John - disconnected, unsure of what Sam wants from him. He's tried to be what he thinks Sam wants, as he did with John, but it isn't getting Dean approval from Sam - or love.
This picture is symbolic of that shift - of Dean losing that big brother role he's always held with Sam. At the moment, in Sam's life, Dean feels burry and in the background. The irony of course is that Dean is central to everything Sam is doing.
In this picture, Sam might be re-enacting something of him and John. How he wished it might have been. But I think more than that because while Dean wanted to be John - Sam wanted to be Dean.
Sam: Yeah, because I've been following you around my entire life. I mean, I've been looking up to you since I was four, Dean. Studying you, trying to be just like my big brother.
With Adam he gets a chance for a moment to achieve that - to be just like the big brother he has looked up to all his life. Teach Adam to look after himself, teach him to hunt. Of course he fails in this too, although of course Adam is already dead, and it is Dean who has to rescue Sam.
And there is a darker side to this...
Sam: You've saved my life over and over. I mean, you sacrifice everything for me. Don't you think I'd do the same for you? You're my big brother. There's nothing I wouldn't do for you. And I don't care what it takes, I'm gonna get you out of this. Guess I gotta save your ass for a change.
Two seasons later we are truly seeing how deeply Sam meant that. Right now? Sam is willing to sacrifice everything - himself, his humanity - for Dean.
And that's something he learned from both his father and his brother.