I think that the problem may be with the term "slowing down."  I think a
more precise term might be "less kind of the action that appeals to North
Americans."
 
The physical play has already been mentioned.
 
The larger ice surface also "slows down" the game in that there is less
frequent action in front of the goal.
 
There may be a lot more perimeter play, including behind the net.  If the
defensive team tries to defend the entire defensive zone, they may leave
gaps in the slot area, especially if the other team is quicker.  So they may
be inclined to play something like a shorthanded situation, conceding the
perimeter and concentrating on protecting the slot.
 
On the smaller surface, the distance from the boards to the slot is lesser,
so that the defensive team may be more likely to contest the perimeter,
since they can still get back to the slot to cover it.
 
To stretch an analogy a bit, note that Europeans enjoy soccer, which
features very few attacks on goal, but a lot of skilled footwork and passing
along the perimeter.  But soccer isn't nearly so popular in North America,
where there is a preference for high scoring, or at least for lots of
scoring chances.  On the other hand, indoor soccer is a more North American
kind of game; you're always in front of the goal
 
There's another thing that my son pointed out to me that I hadn't thought
much about.  With the wider surface, it's a lot harder for the point men to
hold the blue line, so it's easier for the defending team to get the puck
out of the zone.  So an attacking team may be more inclined to concentrate
on possession; once again, think of a power play.  Many people (including
me) don't particularly care for power plays, because the teams tend to hold
the puck a lot, knowing that if the other team gets possession, they'll ice
the puck.
 
Clay
 
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