Right. It's like they always needed a scapegoat on which to place all types of crap, and that was him. But the minute anyone needed help, he was always there.
Her son wasn't going in the way she wanted him to so just needed somebody to blame... that happened to Brian. She's was really berating him too.
If she hadn't lashed out at him, he would not have had to carry on the way he did at Michael's 30th. Sure he could have gone about it better than humiliating Michael and Tracy, but Brian felt responsible or he was made to feel responsible, so he pushed Michael off the cliff.