Why don't all airlines have overhead bin holding rails on their narrowbodies? On newer aircraft, IMO it woudn't make sense not to include them. When Delta installed the bin extensions on their MD
-88s and 757s, holding rails were added on. Delta's 737-800s came with them factory-installed. However, I have noticed that not all 737NGs have them:
To the left is the Continental 737-700 without the holding rail, to the right is the Delta 737-800 with the holding rail. Why isn't this option standard on all 737NGs? I don't see a point why not to include them.