I was reading some of the conjecture spoilers and some of the stuff ignored some of the things that were allready stated in films. Episode IV Ben says of Owen: "He thought he should stay here and not gotten involved. He thought you'd follow Obi-Wan on some damn fool idealistic crusade LIKE your father DID." That means that:
Anakin is on Tatooine at the start of Episode III (opinion). Ben comes back for Anakin and asks for help. Owen is very annoyed and aggitated by this because the Jedi were responsible for taking anakin away from his mother and now their taking Anakin away from his wife. To Owen Anakin has been tortured enough by the political Jedi's. So Anakin leaves his wife behind never to see his kids again.
And don't forget that nobody knows what the death star is in Episode IV. If it was killing planets in the galaxy before IV than everyone would know what it is. Even Tarkin expresses that the station is new. So it will not be completed until the end of III.