As a photo viewer, an iPad is nothing special. It might even be a bit overpriced. As someone trying to sell your services in an environment of heavy conspicuous consumption (newlyweds) you might want to show off the Apple product just to keep up appearances.
An Android is actually the easier device to deal with if you are moving things around. There's nothing like iTunes to get in the way. Just plug it in and drag and drop.
This is about making an impression on the kind of people willing to spend 6 figures on a wedding.