Simon wanted to say that Mal did care, because... well, if he hadn't, he would've left them behind months ago. He'd certainly had enough opportunities. If nothing else, Simon and River's talents had proven useful enough to merit keeping them on board. But Simon still wanted to believe there was more to it than that, and that alone made a part of him think it was true.
"Of course he does," he told River, cracking half a smile and giving a small laugh. "Someone's bound to have gotten hurt by now, and he's got to miss making up things to complain about you to me for."