Zarban wrote:Well, the obvious answer is that Lucas didn't really have Luke and Leia's early life planned out when he wrote Jedi. He sort of vaguely figured Leia's mother took her away to Alderaan while Obi-Wan took Luke away to Tatooine, and didn't think too hard about why. And at the time he probably figured Vader never even knew she was pregnant, which is why he never searched for the children until he encountered Luke.
Indeed, that's what the plan was, as evident in the shooting script and novelisation for ROTJ (source: http://www.angelfire.com/scifi/banthapo … cript.html):
Luke looks into the distance, trying to comprehend all this.
BEN (continuing his narrative)
When your father left, he didn't know your
mother was pregnant. Your mother and I knew
he would find out eventually, but we wanted
to keep you both as safe as possible, for as
long as possible. So I took you to live with
my brother Owen on Tatooine... and your mother
took Leia to live as the daughter of Senator
Organa, on Alderaan.
Luke turns, and settles near Ben to hear the tale.
BEN (attempting to give solace with his words)
The Organa household was high-born and
politically quite powerful in that system.
Leia became a princess by virtue of
lineage... no one knew she'd been adopted, of
course. But it was a title without real
power, since Alderaan had long been a
democracy. Even so, the family continued to
be politically powerful, and Leia, following
in her foster father's path, became a senator
as well. That's not all she became, of
course... she became the leader of her cell
in the Alliance against the corrupt Empire.
And because she had diplomatic immunity, she
was a vital link for getting information to
the Rebel cause. That's what she was doing
when her path crossed yours... for her foster
parents had always told her to contact me on
Tatooine, if her troubles became desperate.
This earlier scene is precisely why Luke later asks Leia about their mother, even going so far as to specify Leia's real mother.
