One of the reasons is that it's not recorded. I agree, that reason is a silly. Not only would Genesis etc. be therefore invalid or whatever, but everyone also argued that The Last Way and Devil Doom should get into the rankings, because it isn't like other games record final boss stats either.
When I said it should be there, I think RPG - though probably others - said it would be a bad idea because it's near impossible to get through a level without being hit. That was quite a while ago though, and I'm sure to be able to get such speedy times you'd need to not get hit anyway.
In fact, I think the fluid ring loss system makes it more interesting to ring attack. Perhaps easier, perhaps not, but at least different.
Someone else said that it would be a bad idea because at least one level has a built in ring limit, that being Circus Park where you can only obtain 400 rings. Well duh, we just don't put Circus Park in the ring rankings.
I am pro Shadow rings division.