FYI, this from WOWInsider in case you're wondering why your Alliance isn't winning Wintergrasp a whole lot...
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For those that don't know, the vehicle counter apparently isn't resetting for the Alliance when a vehicle is destroyed. The result is that, after the initial allotment is destroyed, you cannot create anymore vehicles unless, apparently, the Alliance loses and then regains a workshop, allowing them to make a paltry four vehicles which, once again, do not drop off the counter when they are destroyed.