It's interesting, as Sam and Dean didn’t know Bobby THAT well when they were kids, and he doesn’t seem like the comforting type. Yes Sam turns to him for reassurance as well as Dean. I don’t think we ever see an example of Sam turned to John for reassurance, though.
Sam cuts back on asking Dean for reassurances after the Hell deal, but in a way, the scene in the church in Sacrifice was a big of example of Sam asking to be reassured. When intensely stressed, he falls back on old patterns.