This has probably been discussed in another post, but, when you take into account the total deaths from Alderaan, the Death Star, Owen and Beru, Greedo, various Stormtroopers, Jawas and rebel pilots, this movie has one helluva death toll! And what did we all do? We sat in the audience and CHEERED! This is NOT a film about empathy.
Not only that..:
This Halloween while my friends and I walked all our little rugrats around, I joked how funny it would be to dress up my kid as "The Saw Guy" (I haven't seen the film), my wife and more than one person krinkled their noses and said it would be in poor taste.....meanwhile about 20 little Darth Vaders walked past us.
As for the OP, as someone else said...the fact that he calls them "Aunt and Uncle" says that somewhere along the line Owen and Beru had second thoughts about this whole 'getting a baby dumped on us' thing. Besides we only know Luke was given to them as a baby from ROTS, does it say anywhere in Star Wars (I refuse to call it A New Hope) how old he was when they started raising him?