Copyright Laws 101

In the United States, when the photos are taken then the photographer owns the copyright to the photos. The copyright owner (photographer) has the right to control a list of things, including:
(a) who gets to reprint the photos,
(b) who gets to make derivative works of the photos (such as a painting of a photo),
(c) who gets to sell copies of the photos, and
(d) who gets to display the photos publicly.
It is more customary now that you can pay an extra fee to the photography to buy a copyright license (i.e, permission to do one of the things in (a) through (d)). Usually that license is just for the right to reprint the photos (i.e., use the photos for personal use, such as on Christmas cards or in a wedding photo book). The reason for this fee is that the photographer will lose out on the money that you would have paid her for the prints. Since one of the rights of the photographer is to sell copies and another right is to publicly display the photos, the couple and the photographer can also negotiate how the photographer will be limited in these activities. For a fee, the couple is purchasing those rights (and not just a license) away from the photographer. Sometimes this will not be an additional price in the contract, but it is understandable if the photographer wants to charge a fee for this, to make up for what the photographer otherwise would have made commercially on the photos.