The Stormtroopers are uncaring, merciless dudes, for sure. But - WHY DO THAT?! Even if Owen and Beru were holding out on information, murdering them and BURNING THEIR CORPSES OUT IN THE OPEN is an incredibly weird, malicious choice to make. Hell, even Vader - the baddest dude in the universe - never resorts to defiling corpses for no reason. They don't even bury them - just leave them on the front porch for anyone walking by to find. Real, REAL messed up.
Watch Star Wars again. After Aunt Beru and Uncle Owen are found dead (and their corpses DEFILED), Luke NEVER MENTIONS THEM AGAIN. You can pretty much read Luke's reaction to this all as a happy one - he's finally free to explore the galaxy, join the Rebellion, and do whatever he wants! His stupid, boring aunt and uncle are gone forever and out of his way! Yay!
Seriously - he never once indicates he's trying to get vengeance for them, honor their spirit, or make them proud. He never mentions them by name or even in passing. He's just psyched to not have to drink blue milk and "farm for moisture", whatever the hell that means. And - while this cannot be confirmed - they were probably murdered and their farm destroyed because they refused to give up the location of the droids (and therefore Luke). They probably died to protect their whiny nephew, who was forced onto them by some weird space wizard 20 years ago.
Hey, speaking of people dying and then main characters not really giving a shit - Alderaan. It's a pretty big moment in the film, when you see the kind of firepower the Empire is packing once and for all, but it doesn't have a whole lot of weight to it - at least, not the weight it should have. I mean - AN ENTIRE PLANET GOT BLOWN UP. In, like, a second - an entire civilization was completely wiped out. And our only connection to it is Leia, who grew up there and (presumably) had her entire adopted family die before her eyes.
The weight of that is completely left to Obi-Wan's line about millions of voicing screaming out in terror and then suddenly being silenced, and then it's mostly passed. We don't get any real reaction out of Leia - hell, the next time we see her, she's mostly just sassing Luke (in his Stormtrooper get-up) like nothing's wrong. She's got more immediate problems, sure, but it'd be nice if someone would recognize the MULTI-MILLION PERSON GENOCIDE THAT JUST HAPPENED.