We know Luke cared for Owen and Beru, because he rushed into danger -against Ben's plea - to make sure they were OK. He had a look of horror and outrage when he saw their bodies. The transition to the Death Star is one of the most dramatic in the film, mainly due to the music. When Luke comes back to the sandcrawler, he doesn't even speak at first. Ben's way of speaking to Luke about what would have happened had he been there had the tone of consoling him. Those are all cues that Luke cared and was emotionally affected by what had just occurred.
I've heard that Mark Hamill wanted to play Luke as falling to his kness, sobbing when he saw the burned houses. Lucas wisely told him to tone it done.