You're right.  They're buying a hanging Holstein (so the dressing % difference is already taken into account) which is going to get cut up and go into boxes.  My point is, the meat isn't worth any less.  If they were buying live Holsteins, that would be a different story.
Now, if he wants to give his friends a break on the price because they are Holsteins, that would be a very nice thing to do.  It doesn't make them worth less when they're cut up.