Cersei's conversation with Catelyn at Bran's sickbed & her revelations about her loss of a child in infancy is completely contradicted by her character and doings in the series. According to the books, she never gave birth to a child of Robert's, which is cited specifically as one of the clues that raised suspicions among the court of the true paternity of her children. Only she & Jaime were aware of the one pregnancy Robert begat with her, so as far as anyone knew, it appeared that she had no relationship with her husband, no matter what the facts of the matter. It was speculated at least once in the series directly, that a single child resembling Robert might have put paid to any rumors or suspicion. Note, for example, that four of Catelyn's children resemble Tullys rather than Starks - one more maternal resemblance than Cersei has, but because she has a child who is said to be unquestionably a Stark in appearance, the thought that she has conceived them with Edmure or Brynden never occurs to anyone.

With this concept in mind, what is the point of adding the conversation scene? The encounter between Jaime & Jon, for instance, serves to flesh out Jaime's character and mannerisms and to show how the Night's Watch is viewed by the more sophisticated and typical southron native. There was a point to adding that scene. There seems to be no such point to adding the scene of Cersei visiting Catelyn. Her attitude is better conveyed at this point by her breakfast conversation with her brothers. Bran's condition was established by Tyrion & Joffrey's conversation. Catelyn's obsessive vigil is later shown in the scenes with Jon & Robb, and not added to by her talk with the queen. In fact, her behavior is so normal and typical of a mother at her child's sick bed, that IMO, it undermines the obsessive nature of her care for him later shown in the scenes with the boys. Since the first thing we see is a couple of mothers sharing their apparent grief, (and knowing Cersei's part in Bran's injury, her hypocrisy makes her the villain of the scene, diminishing whatever subtle faults in Cat's behavior) that remains with us and dilutes her wretched treatment of Jon and justifies her behavior with Robb & Luwin. The legitimacy (and comparative moderation) of her grief is supported by the scene with Cersei, so Robb comes across as something of a jerk for diminishing her care. His older portrayal doesn't help, either. The practically unchanged conversation from the books is less significant when an apparently grown man relieves his grieving mother of her duties or remonstrates with her for her neglect of her other son. When a 14-year-old boy has to do those things, the fault in Catelyn's behavior is more clear, as is Robb's apparent maturity and ability beyond his years. Cersei's "me too" scene, in my mind, spoils the portrayal of Cat, and by extension, Robb, to a certain extent.

Given the otherwise better handling of the changed scenes and added conversations, I have to think there is a purpose to their addition of this incident. Either to generate unnecessary sympathy for Cersei (who is probably the single character most undeserving of sympathy in the whole SoI&F and who already garners the most wrongly directed sympathy without any help from the TV writers) by adding either a "more human" side to her and reinforce how greatly she fears any further threats to her offspring or an additional rationalization for her resentment of Robert, or else the scene was added to instead make the revelation of her evil all the worse when finally exposed - recall in the books, she aborted the one child she conceived by him. Is this an indication that her infanticide on the show is of a kind recognizable by ALL readers, and not just the pro-life crowd? Could they be taking extra care to rub her evil in the faces of an audience that of the books was too prone to falling into the PoV trap and accepting her rationalizations of her crimes at face value? Will they have the guts to make her so spiteful to her husband and obsessed with her brother than she would go so far as to actually poison a child of her flesh because he is Robert's and not Jaime's?

Another interesting point - the pronunciation of maester is established in this episode, and coincidentally, Maester Luwin is also apparently the reader of the books on tape. Angel fans may recall him looking a bit different as Roger Wyndam-Price, Wesley's psychologically abusive father.