From inquiries I've made elsewhere, it seems no one has a strong answer as to why the ring-with-ears is on that lens. You will not that the ring has two red dots opposite each other, and the idea is to rotate the ring so that one of the red dots is aligned with the larger red dot on the actual lens mount -- this larger red dot being the one you line up with the dot on the body itself when you mount the lens. When all this is done, the ring-with-ears is perfectly aligned to enter the lens chamber without hitting anything. However, when the lens rotates either in mounting or when focusing the ring rotates as well, and the ears hit the top and bottom of the lens chamber. The lens then continues to rotate, with the ring-with-ears rotating on the lens. It doesn't hit on the interior of my Nikon S2.

I can only suppose that someone, for some reason, thought the ring-with-ears served some purpose, perhaps, as you say, in protecting the rear element in some fashion. It really strikes me as being something on an unnecessary "appendix" that might be removed without causing any harm. In my lens and camera, the ring-with-ears does cause a bit more drag when focussing, but it's not significant. If I felt comfortable taking it off, I probably would.

FYI, I'm sending my IIa to a repairman for a CLA, and I may ask him why he thinks the lens is built like that. It's a Zeiss mystery.