I understand the need to have coaches dress neatly. If NBA coaches were going the way of the Belicheck style sleeveless hoody, fine, change the rules. However, SVG dressed neatly and professionally. Whether he's wearing a button-down or a turtleneck, it doesn't make a difference to me.
It's the same thing with the players' dress code: I appreciated the fact that the players are given at least some discretion in how they can dress, even if it's significantly more limited than it used to be.
http://www.nba.com/news/player_dress_code_051017.html For instance, at games, a player can wear designer jeans, a sweater, and a sport coat, if he wants, or he can wear a full suit. I think coaches should be given similar discretion (except for maybe the jeans).