It wasn't thought all the way through, and doesn't mesh with the OT as a result. Had the films been made in chronlogical order, it would have made more sense for Ben to raise (and train) Luke by himself on Tatooine instead of waiting twenty years in the shadows, and letting Luke bond with Owen and Beru. You don't put Luke in the same scenario as the padawan whose training you botched! Yoda could have raised Leia on Dagobah instead of putting her in potential peril of crossing paths with Palpatine and Vader too soon. Not that either one ever picks up Force vibes from the young Senator from Alderaan.
