Guy dumps the puck in from two feet behind the red line. No ice. Close enough. Not even controversial.
Given how fast the game is now, could you argue that a missed icing call is as material as a missed offside call?
Because icing is situational, offsides is not. The officials play the advantage -- they have the sole discretion to wave it off if it has no direct impact on the current play.
Icing doesn't occur in a vacuum. It's not just about the icing itself, it's also about the position of the players when the icing is executed. Linesmen are more inclined to let icing go if there is no forecheck or pressure. The team is icing to give up possession (usually to have a line change).
From the perspective of the defending team, if you give them the option to take possession in their own zone or take a faceoff in the offensive zone, they'd likely choose the possession every time (since the faceoff is a 50/50 gamble at possession). So the linesman is essentially making that decision for them. Don't blow the whistle if the d-man is not being pressured, they want to have the puck.
If, on the other hand, icing is executed as an attacking strategy ie: to gain territory, dump and chase, sending in forecheckers to retrieve the puck behind the goal, then icing is called far more tightly, as tight as offsides. They're using it to gain a distinct advantage so the puck better be over the redline when executing that strat.
So the next time you see a dump-in from behind the red line, look where the players are and what they are doing at that moment. The linesman usually has a good reason for letting the icing go, and that reason rarely has anything to do with the icing itself.