Now the Bruins and their fans will always find excuses or reasons to lay blame on others, but let's be lucid about this development.
First, Zdeno Chara could barely skate in this series. I'm not impartial when it comes to this beast, but I've been saying for a while that his mobility is waning, and it was flagrant in the later games. His finger isn't the reason he was ineffective. He looked like death on skates in Game 7. Since he's 37 years old, it wasn't a big leap to wonder if the Canadiens were just too fast for him to keep up.
And let me re-iterate that for a Norris Trophy candidate, the fact that he doesn't play defence on the powerplay, but that they rather put him in front of the net as a screen, is a dead giveaway that this guy can't play very well any more.
As far as the slash itself, it's far from cut and dried how dastardly the Canadiens were in this instance. The NHL allows 'light' slashing in its rulebook.
61.1 Slashing - Slashing is the act of a player swinging his stick at an opponent, whether contact is made or not. Non-aggressive stick contact to the pant or front of the shin pads, should not be penalized as slashing. Any forceful or powerful chop with the stick on an opponent’s body, the opponent’s stick, or on or near the opponent’s hands that, in the judgment of the Referee, is not an attempt to play the puck, shall be penalized as slashing.
Note how the first sentence in 61.1 conflicts with the second. On the one hand, you can't swing your stick at an opponent, even if you don't even touch him (reminder: send memo to Duncan Keith). On the other hand, it you're swinging it "non-aggressively" in the pants or shin pad region, fair game. Good luck parsing that one, NHL referee.
The RDS boys showed the Michaël Bournival slash on Chara earlier in the series during an intermission, and he did land it where it hurt the Bruins' morlock, but it was well within the acceptable boundaries of NHL play, as extolled by Nick Kypreos or Randy Carlyle. It was a fly-by 'finish your check' slash, a 'let them know you're there' slash, not an egregious, Bobby Clarke on Mikhail Kharlamov ankle-breaker.
So while Mr. Chara's injury is unfortunate, it's what the NHL and its hype machine decrees as the cost of doing business. Slashing isn't really slashing, it's tight, defensive, grinding, close, hard-fought playoff hockey, the party line goes. Until the Bruins' captain's finger explodes, then the Bruins can start whining