First, a couple of people have pointed out that Leia could have a few sources of information that Luke doesn't, since she's raised by someone who knew her mother well, having served with her on the Galactic Senate. Baal Organa may have given her enough information--including, perhaps, pictures/holograms/visual records of her mom--that she formed more of a connection with her, whereas Luke was raised by people who were more connected to his father, and therefore Luke formed more of a connection with him.
A poster at the Galactic Senate forums said:
As a lot of the dialogue from the novel shows, the Force works in a way that even the Jedi don't completely understand. It just happens that Luke goes down his father's path, while Leia goes down her mother's path. They even play similar roles to each other, like Leia being the person that almost "causes" Luke to turn at the end of RotJ, just as Padme "causes" Anakin to turn in RotS. In the OT, the Jedi seem to depend more on the will of the Force in their decision-making - they don't train the twins from infancy, they hide them away, and let the Force guide them to them. It just happens that Luke is the one who is guided to them first, and brought to Obi-Wan - ironically, through Leia's coming to Tatooine. It was all the will of the Force, just what brought Qui-Gon to Anakin in TPM - and it seems that, for whatever reason, the will of the Force creates a strong connection between Anakin and Luke, and one between Padme and Leia.
*nods* I can live with that.
ETA: Oh, I'm so amused. I liked the explanation of the poster I quoted above so much, that I did a search for his(?) other posts. One of the first ones I found was in the GS's off-topic area, in a thread about Harry Potter. And guess what this poster was asserting in that thread? That Harry and Ginny will fall in love. :D
ETA 2: Oh, I like what he says about that so much, I'm gonna quote it, too. I am so bad. Quoting stuff from a members-only forum on a public LJ post without the author's permission. Bad Joie. Bad. This poster goes by the name GeneralDirection, BTW (at least I can't be accused of not giving credit):
I think it's extremely possible that Harry will end up with Ginny - the irony was that, although in OotP her romantic feelings for him seemed to have ended, there's a huge difference between a childhood crush, and a deep and lasting love. There was a recurring thing in OotP where, if Harry was feeling bad about things or down, he would talk to Ginny, and somehow she would make him feel better about things. They developed a friendship in that book, and Harry confides in her a few times, when he doesn't want to talk to anyone else. One scene that interested me was in the library, after Harry had seen his father through Snape's Pensieve. Harry finds himself stuck for words at one point, and also, for no reason he can explain consciously, finds himself feeling better about things. This is a big contrast with Cho, who Harry often felt angsty and insecure about - Cho often made Harry feel worse about himself, but Ginny seems to make him feel better about himself. Also, there's an interesting metaphor that seems to run through all the books, about Snitches. JKR seems to have associated them with romance, for some reason. In PoA, Cedric gets the Snitch ahead of Harry - a foreshadow that, in GoF, Cedric will get together with Cho before Harry. In OotP, we see James playing around with a Snitch, purposely in full view of Lily. Then later on, the easter egg Ginny gives to Harry is decorated with, yep, Snitches. Finally, at one point in the book, Ginny catches the Snitch just ahead of Cho. Maybe it's just all coincidental, but you never know. wink.gif At the moment, I think it's most likely he'll be with Ginny. Hermione is still a possibility, of course, but somehow their relationship seems to be more of a brother-sister bond. Of course, such a deep friendship bond is a vital part of a relationship, but all the hints so far seem to point to Ron and Hermione, and there's no shortage of chemistry between them. As for Luna, she seems like more of a storytelling afterthought for OotP, simply to solidify the theme of hope and belief that things will turn out OK, even though it looks impossible - I think it has to be someone who's been there since very early in the story. It's too late for JKR to introduce a new character in HBP and have us emotionally connected to them enough to want her and Harry to fall in love. The hints with Ginny have been subtle, but almost classic romance, such as her chasing after the train and crying in the first book.
The interesting thing about these plots is that JKR is a big fan of Austen, and seems to be following an Austen-type pattern for her romances. The people who are "right" for each other start out either by disliking each other, having a combative relationship with, or by just ignoring each other, or maybe there is unrequited love from one. Instead, the main characters are in love with people who are wrong for them, halfway through the story (GoF - Cho, Fleur, Krum) - but eventually, a connection grows between the people who are right for each other, normally at the very end - so my guess is things will only come together fully in Book VII. But we'll see a development of the stories in HBP that should make it obvious where it's going.
Yeah, lots of stuff we've heard before, but he gives a little more support for using the Snitch as a romantic symbol than I've come across before. Hey...GeneralDirection isn't any of you, is (s)he?