Pure craziness here! He hasn't made a philosophical change man, the system the team plays has changed, and Boro has been given a more rounded and less scripted defensive role.
It has everything to do with toughness, grit and glue. Every single time Boro is mentioned by anyone team related they gush over his toughness (the taking the pain and gutting it out kind), his hits, leadership etc... The above stuff is still there, and what got Boro to the NHL, the change in GBs system, and the refocus of Boro to play a more rounded game means that he has the chance and support to show case his other (albeit limited) defensive skills.
Without his hits, grit, toughness, and locker room glue character, Boro would not be in the NHL, even with his much more effective play this season. The better play has made him a solid roster player for the team (instead of the incessant 7 d-man talk) who can contribute in more ways to the team, and more importantly shut this forum up about him for a year
I agree with the idea that he doesn't need to focus on fighting, he's not great at it, though fearless, and it's not actually the best use of his skills. I think the freedom to play a more rounded game means that he doesn't feel like he has to fight guys to stay in the league anymore. He seems to like hitting, and knows that it's his bread and butter.