I’m sure that he made that comment intentionally to motivate Marbury. It also doesn’t hurt to make a team leader whom everyone expected to be cut feel wanted.
Bottom line is that the biggest things the Knicks needed were defense, a more efficient offense, and a positive environment. Larry Brown must first establish that positive environment for his strategy changes to be effective: he has to convince the Knicks that if they buy into his philosophy and work like a team they’ll win games. Think of when Isiah first took over, got Marbury, hired Wilkens and suddenly the Knicks came to life and played like they wanted to win, and as a result won. Or when Van Gundy left mid-season and suddenly the Knicks started to play as if they were just happy to there, and as a result lost.
If Brown leaves things exactly how they were last season and lets Marbury and, less so, Crawford lead the team while running wild, the necessary on-court improvements cannot occur. If team leadership is in the hands of tested veterans like Houston and Rose, who will play the way they are asked, it’s much easier to get everyone on board then when your team leader belittles his teammates for missing shots and does not play defense. Ideally, Marbury, clearly the team's most talented player, will then be motivated to earn a leadership role and become the best player.