Depreciation costs are part of ownership. They are arguably the most expensive part of owning a car. Not maintenance, not insurance, not fuel, not anything else.
Depreciation of a heavy duty truck will be 10's of thousands. It could buy a lot of engines, transmissions, tires, brakes, fuel. You know, the items everyone likes to fret the most. Many get worked up about MPG ratings within a few points of each other, or potential minor problems in the future, but then look the other way at the value flying out the window every time the wheels turn.
That said, considering depreciation cost in the decision is wise.