Shouldn't he be a bit more, I dunno, grieved? I don't know how many times I've seen this movie since I was a tiny little boy, probably hundreds, but somehow this occurred to me only recently. I can't be the only one who noticed this.
In reality? Yes. However, having him grieve and be all mopey would have ruined the film. Nobody wants to watch some guy we don't know grieve over two people we know even less. Luke grieved more over Ben because we, as in the audience, knew Ben.