Sam has fully expected Castiel to be listening. Anybody who doesn't expect him to listen is an idiot. After all, it's his life that they're talking about, in broad strokes.

He smiles and would have responded had Balthazar not offered him THAT. It takes a moment for Sam to get his head around it before looking to Castiel to see what he thinks. "I can't say that I would mind, as long as Castiel is happy to do so."