Every company has "criteria". Many companies have the exact same criteria. The assumption that because they are all of the same "type" of car does not hold up when you step back and take an unemotional look at the picture.
may have been 2-6 vehicles onsite that all looked the same
At the same time, there may not have been 2-6 vehicles onsite that all looked the same. Funny, when you drive the Lockheed plant there are a lot of "sedans", "mid-sized" even. Does that mean everyone is renting?
I am not sure what you are getting at but any type of vehicle can be rented. The rule is "most economical means", which limits expense on tax payers and ultimately the crown. It varies from city but here is the options for Windsor,Sedan Budget Rent a Car/AVIS/Discount Car And Truck Rentals.