actually you are wrong...
early weaning calves pays in two ways..
1- for those who sell young calves in public auction-- if you wean and get that calf on a good, high fat, show type ration-- you are going to have less stress, more bloom, and in general-- higher valued calves come sale time-- especially compared to those who will pull the calves off mom the week before the sale. Fact of life-- grain puts pounds on-- milk only does to a certain amount-- but most of it is 'white meat'. That's why the people who creep their calves have such good luck-- best of both worlds. Think of it this way-- those calves will be out with the cow eating grass instead of in a barn lot on a self feeder-- grass does not equal good gains in show calves. Show calf people don't care about grass, that' the poor man's foodstuff.
2- it's far cheaper and easier to feed the calves-- than it is the cow. kick her out to grass and forget about her. I just read a study where you saved over 1/3 of the feed costs associated with graining calves- as compared to their mothers and/ or calves both.
I've been thinking of this for a couple years now- and finally made the plunge. Weaned my babies half the age they normally get weaned-- and they look tremendous, better than they've ever looked.