I remember when the Jets reentered the league in 2011. They were getting interference calls left and right because any attempt at impeding a forward's progress into the offensive zone after a dump in was considered interference. Now, almost nobody gets called for that.
This ties into the second point, that someone else touched on in this topic already - the fact that powerplays are down by half since 2006.
The third one, and probably the most relevant one, is that the distribution of ice time has changed since 2006. Your 4th Line is no longer getting only 3 minutes a night, with your top line getting 24 to 27 minutes tonight. Coaches are spreading the ice time around to keep players fresher longer. That means your stars aren't going to be on the ice as often, so they won't have as many opportunities to score goals.