I recall reading that the ecoboost EL 4x4 had mechanical LSD standard but just looked at my 17 window sticker and don't see it listed. Even with an open differential in the rear, the traction system will use the ABS as a quasi limited slip in front and rear, which supposedly is better than a mechanical LSD for all but the most die hard off road conditions. But let's be honest, what kind of extreme off road conditions did Ford imagine a long wheel base 6400 pound expedition would see in its typical lifetime operation?
There is a YouTube video of an F150 without e-lsd doing a burnout with one wheel on pavement and the other on dirt, and both wheels were pulling. It was a demonstration of the abs simulated LSD.