I know a Mercedes dealer principle quite well and he noted that on many models, residuals were pretty stable, but as the ML sales tanked in 2001-2002, MB-Credit fiddled with the residuals almost constantly to try to come up with a lease that would work and not leave them high and dry at the end of the lease. MB-Credit lost tons by overestimating residuals on the 98-99 models as most folks returned the cars and since values had dropped, the financing arm ate the difference.
Perhaps given Ford's giant dealer base and massive number of models, they take a more methodical approach?