Thousands of passengers were stranded at Cairo's airport on Saturday as flights were canceled or delayed, leaving them unable to leave because of a government-imposed curfew. Several Arab nations, meanwhile, moved to evacuate their citizens. As Egypt's unrest neared its sixth day, the cancelations of flights and the arrival of several largely empty aircraft appeared to herald an ominous erosion of key tourism revenue for the country, hitting hard at its pocketbook even as protesters centered many of their grievances on the grinding poverty they endure daily. Europeans and Russians account for a major chunk of the tourists to Egypt,...