Yeah, there are inconsistencies between the twins' births and what they remembered a generation later on Endor. The real reason is that Lucas hadn't sorted out all the details yet nor decided how he'd depict Luke and Leia in any prequel films were he ever to get around to making any of them. Now you're left wondering how a newborn Leia just minutes old remembers her mother's sad expression as she died on the delivery table but Luke doesn't. Like you said, Luke had no memory of Padmé but if Leia picked up a Force image/impression of her mother in the moments after she was born then why didn't her brother? And did she at all during those brief moments?
There are moments in the Saga where I try to adopt the MST3K approach: it's just a movie, we should really just relax.
's retcon: Leia's memory of her mother was just a Force vision she had when she was very young, cf Yoda's, "old friends, long gone."