Ethical breeders breed healthy sound dogs to other healthy sound dogs. They will be targeting the standard. They will usually be more likely to hang on to larger girls than they will larger boys, but the overall health, soundness and temperament are key.
Less ethical breeders who like to churn out puppies tend to love to have access to smaller boys and larger bitches because yes it makes the odds that they will produce small (for a buyers marker higher) and the risks of C-section less likely, and thereby also the cost of the litter smaller. Some also believe that larger bitches will have more puppies.
In the end the reasons for smaller studs and larger bitches varies. But in general I would recommend not seeking breeders who seem to heavily focus on using small studs and large bitches. Again, I would hope that a breeder would be more focused on more important issues than size.