In one sense they are, but there is a difference between a photograph being your property and the information it contains being your intellectual property. You own the files and any prints, albums or DVDs you receive ash part of your commission. As mentioned before, copyrights aren't the only rights that exist and your ownership of the deliverables given to you by the photographer is protected by the law and you own the rights assigned you by the photographer, just like how when you purchase a music CD, you pay to listen to or display the material and your rights to do this are guaranteed even if you don't own the copyright.

According to UK intellectual property law any creative works are automatically copyrighted to the creator, except for in circumstances where the creator is an employee creating the work under his or her employment. Copyrights can be reassigned only by stating this explicitly in writing, though most professional photographic bodies and agencies strongly advise against transferring copyright.

It is important to note that you still have rights over the images, you paid for them and the fact that you don't own the copyright doesn't mean you have been undersold; copyright is only one of the ways in which a person has rights over the images, and copyright is the only right which the photographer is permitted to retain.