How many times have you dropped your binoculars on the eye cups and had to replace them? I have never dropped any of my binoculars. An eye cup get's used a lot going in and out and in my experience metal will last longer and is smoother because it can me machined more precisely to closer tolerances. I will take metal eye cups and a magnesium body on my binocular over plastic any day.
Dennis ..... You got to keep up, you are falling behind.
From less than two weeks ago ............
"I expect it to hold up just fine so long I do not have a significant accident with it. So far, I have never dropped one (knock on wood!). If something bad does happen, then I will get a chance to test out the Nikon No Fault Policy!"