Diana,
a number of labs require an application -- White House does too. I believe it's because they are commercial labs and want to be sure the folks using their services will provide the volume necessary to make the discounted prices profitable and will also be able to provide good files to print. With services like EZ Prints for example, they are willing to deal with the onesy-twosy orders. The major pro labs are looking for folks with wedding or event volumes or who will be ordering high-end products like books and large prints.

Jim