The overall vehicle amount has not increased or decreased. However, the spawn tables have been modified to take into account people spray painting their vehicles to less noticeable colors. During a zombie apocalypse I find it doubtful that people would deliberately drive around in brightly colored cars if they could avoid it. The other change is the amount of HMMWVs. I also find it doubtful that the Army has so few vehicles to conduct business with. If they had that few (originally) then I believe they would be considered a very ineffective Army. Mobility matters for an Army.