In T2, the 'good' terminator was programmed to take orders directly from John. Remember, the terminator didn't want to go break Sarah out of the mental hospital-he knew it would be dangerous. So obviously, the terminator wasn't programmed to take orders from Sarah, otherwise he would have tracked Sarah down first instead. And since the terminator's mission was famously "to ensure the survival of John Connor," he had to take orders from the young John. There was no one else to take orders from, and that terminator needed direction in order to successfully complete his mission. The terminator from T2 didn't have emotions, and John had to flip a switch in the terminator's head so that he could learn.
Cameron, however, doesn't need to take orders to protect John (or Sarah). She has already been shown to have at least some degree of emotion, and is certainly able to learn. Whereas the T2 terminator wouldn't necessarily be able to handle the mission on his own without taking orders, Cameron can take the initiative in a situation. Also, in T2, the terminator didn't have any ulterior motives; Cameron might. In T2, future John didn't have any side goals; he just needed to protect his past self. In this series, future John may very well have alternate goals that need accomplishing--goals which Cameron can't tell present John or Sarah about. If you recall, in T2, preventing Judgment Day wasn't on the terminator's list of priorities--Sarah had to have John order him to do that. This time, however, preventing Judgment Day looks to be rather important, both to Cameron and to Sarah and John. Completing that mission might require that Cameron not disclose certain details to John and Sarah--for example, stopping Judgment Day might well be more important to Cameron than ensuring Sarah's survival.
EDIT:
Also, I just thought of a funny solution to why Cameron didn't act like a "freak" in the pilot: future John told her what to say. We know that future John had talked to Cameron before she went back in time--apparently, they had time to talk about the bedtime stories Sarah read to John. Future John could have given Cameron lines to say to his present self and have her stay "in character" when they met. I doubt they'll make any reference to the issue now, but it make for a funny scene: "...So...I WAS HITTING ON MYSELF?!?!?!"