What really makes this incident any different than the second incident last season (the one that earned Allen a reprimand from the ACC)? After that,
Coach K said the following:
So why the reversal by Coach K after one more incident that occurred 10 months later? Could it be because of the difference in the season situations?
Last year: 2nd tripping incident in FSU game. 3 regular season games remaining (@PIT, Wake, UNC). Duke was 'just' (for Duke) 10-5 in conference at the time and had a lot less talent on the roster than they do this year.
This year: ACC season hasn't started. Next 3 regular season games all likely easy wins with or without Allen (@VT, GT, BC).
Basically, it looks like Coach K felt he couldn't afford to suspend him last season, so he defended that the action shouldn't require a suspension... but this year he can afford to suspend him, so now Allen's actions "aren't consistent with the standards of Duke basketball."
ETA: Allen is really lucky no opponent has punched him in the face over his dirty play. Heck, he's lucky none of his teammates have done it... (or maybe they have in practice and we just don't know it).