Ill argue that theres a line in the sand, frosted ears don't always mean frozen feet. There seems to be a point where they can loose ears and a bit of tail, and still have decent feet. Weve got an old cow with barely any ears and shes solid as the ground she walks on. Frozen feet usually happen when theyre still soft, but after that theyre usually good. 

Ill agree that frozen feet are not good in the feedyard, but it also depends on how bad, some just get a little longer toe and are fine, but some are bad and that's when they don't do well. 

Just my opinion from raising our own calves and seeing performance in the feedyard. Id take a short eared calf over a rattail grey though