Let me add another thing to consider. While it is possible to go beyond pop cap with the US faction more easily, I have never seen or played a match where this had any impact. Furthermore the faction design also has the drawback that capturing an abadoned vehicle always means the loss of the field presence of the squad that captures the vehicle. Of course you can later abandon the vehicle but you loose an infantry unit for the time it mans the vehicle.
This mechanic makes capturing abandoned vehicles in addition riskier: Most abandoned vehicles are heavily damaged and in most cases can be destroyed quickly. The destruction of the vehicle always means the loss of the entire squad.
In summary, the faction design allows the US forces to go over pop cap more easily, but has so far to have any significant impact. On the other hand, the same faction design has 2 rather obvious drawbacks, one if which increases the risk of loosing a squad at the off chance to secure a tank that was abandoned. I would argue that these two points will impact a game more frequently than the ability to more easily exceed the pop cap level.
Nice point. I've lost several squads of upgraded rifles attempting to steal various abandoned tanks. Other factions would have been able to take those vehicles and still retreat the rest of the squad.