There was an EXTREMELY ****** EU explaination for this. Be prepared to go chest deep into crap!
In some comic, Luke is about 1-2 years old. It's a quiet morning on Tatooine. Suddenly, as Beru is picking mushrooms off the vaporators, Darth Maul, with a robotic lower half attacks them. Yes, you read that right. DARTH MAUL WITH A ROBOTIC LOWER HALF. He was sent to kill Luke, I think.
So Obi-Wan appears (already looking like Alec Guiness, even though this is supposed to be 1-2 years after ROTS), and after a while, defeats the robotic Maul. Owen yells at Obi-Wan about the whole Maul thing being entirely his fault, and tells him to stay away from Luke forever.
So yeah, pretty crappy explaination there. Hopefully this helps some.