The altar was old. It was ornate. And it was on the gambling floor of the Hard Rock Hotel and Casino in Las Vegas.James Lang was startled when he saw it there. Lang, vicar of parishes for the Roman Catholic diocese in Syracuse, had a chat with the manager about desecration. The altar eventually was removed."They thought it looked cool," Lang remembers.It also looked like part of a growing phenomenon: Religious artifacts are migrating as America's shifting population leaves empty churches across the Midwest and Northeast. This March, New York City's archdiocese recommended shutting 31 metro parishes, and Boston has...