I think a lot of it stems from a deal that she made with Luthor a while back - perhaps a feeling of guilt for not telling Clark about it? Another reason is her dad died in Our World's At War whereas Clark thought his dad had died and later found out he was still alive - I think the writers are trying to show that Lois is feeling alone with her dad gone and doesn't feel it's right she lost her dad and Clark's is still alive - trying to get close to her mother and help her grieve also. That's the feeling I've been getting from it at least.
"Never give in--never, never, never, never, in nothing great or small, large or petty, never give in except to convictions of honour and good sense. Never yield to force; never yield to the apparently overwhelming might of the enemy."
- Prime Minister Winston Churchill
"Si vis pacem, para bellum."