These very strong rings are to prevent the crankarm from going too far up the spindle taper, which can at some point cause multiple problems. This is for the driveside only.
I would think that the bolt head bottoming on the spindle end would accomplish the same thing, but the crankarm always bottoms first on the steel ring when using a Shimano crank.

I've had customers machine down their crankarm to avoid contacting the ring so the crankarm's taper could be tightened on a bit further on a heavily-used crankarm. The steel ring will not be easy to remove, it's really on there!