Perhaps since Ford is planning the Expedition to be used for fleet customers more than the Navigator, they have included the engine hours and engine idle hours feature in the display. From page 117 of the Expedition manual:
Gauge View - Allows you to select between either Turbo Boost or Transmission Temp gauge.
• Tire Pressure - Shows the tire pressure. See Tire Pressure Monitoring System (page 359).
• Digital Speedometer - Shows a digital display of your vehicle speed.
• Engine Information - Shows engine hours, engine idle hours and oil temperature.
• Transmission Temp - Shows the transmission temperature value.