You're not out of the runnings until you receive a rejection letter.
If the firm called your friend back and you still haven't heard, it probably means either that your rejection letter is in the mail, or more optimistically, that they liked you enough to keep you around for further consideration, but not enough to call you back in the first round of interviews. If your classmates don't get offers, or if they receive offers and promptly reject them, you may then get the call.
As your experience demonstrates, in many instances, good grades just gets you the interview, and after that, whether you get a call back depends largely on your performance in the interview. That said, I do think there is often a sliding scale of sorts. By that I mean that a student from Harvard or from a lesser school with great grades, for example, can get away with a lot more than less qualified candidates.